[PATCH] Segments can span multiple clusters with tap:qcow

[PATCH] Segments can span multiple clusters with tap:qcow

[Mark McLoughlin]

[-- Attachment #1: Type: text/plain, Size: 479 bytes --]

Hey,
	In blktap's qcow we need split up read/write requests if the requests
span multiple clusters. However, with our MAX_AIO_REQUESTS define we
assume that there is only ever a single aio request per tapdisk request
and under heavy i/o we can run out of room causing us to cancel
requests.

	The attached patch dynamically allocates (based on cluster_bits) the
various io request queues the driver maintains.

  Signed-off-by: Mark McLoughlin <markmc@redhat.com>

Cheers,
Mark.

[-- Attachment #2: block-qcow-multiple-aio-requests-per-segment.patch --]
[-- Type: text/x-patch, Size: 4892 bytes --]

diff -r 33e22185002a tools/blktap/drivers/block-qcow.c
--- a/tools/blktap/drivers/block-qcow.c	Wed Apr 25 13:50:20 2007 +0100
+++ b/tools/blktap/drivers/block-qcow.c	Wed Apr 25 21:32:37 2007 +0100
@@ -55,7 +55,6 @@
 
 /******AIO DEFINES******/
 #define REQUEST_ASYNC_FD 1
-#define MAX_AIO_REQS (MAX_REQUESTS * MAX_SEGMENTS_PER_REQ)
 
 struct pending_aio {
         td_callback_t cb;
@@ -146,18 +145,37 @@ struct tdqcow_state {
 	AES_KEY aes_encrypt_key;       /*AES key*/
 	AES_KEY aes_decrypt_key;       /*AES key*/
         /* libaio state */
-        io_context_t       aio_ctx;
-        struct iocb        iocb_list  [MAX_AIO_REQS];
-        struct iocb       *iocb_free  [MAX_AIO_REQS];
-        struct pending_aio pending_aio[MAX_AIO_REQS];
-        int                iocb_free_count;
-        struct iocb       *iocb_queue[MAX_AIO_REQS];
-        int                iocb_queued;
-        int                poll_fd;      /* NB: we require aio_poll support */
-        struct io_event    aio_events[MAX_AIO_REQS];
+        io_context_t        aio_ctx;
+        int                 max_aio_reqs;
+        struct iocb        *iocb_list;
+        struct iocb       **iocb_free;
+        struct pending_aio *pending_aio;
+        int                 iocb_free_count;
+        struct iocb       **iocb_queue;
+        int                 iocb_queued;
+        int                 poll_fd;      /* NB: we require aio_poll support */
+        struct io_event    *aio_events;
 };
 
 static int decompress_cluster(struct tdqcow_state *s, uint64_t cluster_offset);
+
+static void free_aio_state(struct td_state *bs)
+{
+	struct tdqcow_state *s = (struct tdqcow_state *)bs->private;
+
+        if (s->sector_lock)
+                free(s->sector_lock);
+        if (s->iocb_list)
+                free(s->iocb_list);
+        if (s->pending_aio)
+                free(s->pending_aio);
+        if (s->aio_events)
+                free(s->aio_events);
+        if (s->iocb_free)
+                free(s->iocb_free);
+        if (s->iocb_queue)
+                free(s->iocb_queue);
+}
 
 static int init_aio_state(struct disk_driver *dd)
 {
@@ -166,6 +184,12 @@ static int init_aio_state(struct disk_dr
 	struct tdqcow_state  *s = (struct tdqcow_state *)dd->private;
         long     ioidx;
 
+        s->iocb_list = NULL;
+        s->pending_aio = NULL;
+        s->aio_events = NULL;
+        s->iocb_free = NULL;
+        s->iocb_queue = NULL;
+
         /*Initialize Locking bitmap*/
 	s->sector_lock = calloc(1, bs->size);
 	
@@ -174,13 +198,26 @@ static int init_aio_state(struct disk_dr
 		goto fail;
 	}
 
+        /* A segment (i.e. a page) can span multiple clusters */
+        s->max_aio_reqs = (getpagesize() / s->cluster_size) + 1;
+
         /* Initialize AIO */
-        s->iocb_free_count = MAX_AIO_REQS;
+        s->iocb_free_count = s->max_aio_reqs;
         s->iocb_queued     = 0;
+
+        if (!(s->iocb_list = malloc(sizeof(struct iocb) * s->max_aio_reqs)) ||
+            !(s->pending_aio = malloc(sizeof(struct pending_aio) * s->max_aio_reqs)) ||
+            !(s->aio_events = malloc(sizeof(struct io_event) * s->max_aio_reqs)) ||
+            !(s->iocb_free = malloc(sizeof(struct iocb *) * s->max_aio_reqs)) ||
+            !(s->iocb_queue = malloc(sizeof(struct iocb *) * s->max_aio_reqs))) {
+                DPRINTF("Failed to allocate AIO structs (max_aio_reqs = %d)\n",
+                        s->max_aio_reqs);
+                goto fail;
+        }
 
         /*Signal kernel to create Poll FD for Asyc completion events*/
         s->aio_ctx = (io_context_t) REQUEST_ASYNC_FD;   
-        s->poll_fd = io_setup(MAX_AIO_REQS, &s->aio_ctx);
+        s->poll_fd = io_setup(s->max_aio_reqs, &s->aio_ctx);
 
 	if (s->poll_fd < 0) {
                 if (s->poll_fd == -EAGAIN) {
@@ -198,7 +235,7 @@ static int init_aio_state(struct disk_dr
 		goto fail;
 	}
 
-        for (i=0;i<MAX_AIO_REQS;i++)
+        for (i=0;i<s->max_aio_reqs;i++)
                 s->iocb_free[i] = &s->iocb_list[i];
 
         DPRINTF("AIO state initialised\n");
@@ -946,6 +983,7 @@ int tdqcow_open (struct disk_driver *dd,
  end_xenhdr:
 	if (init_aio_state(dd)!=0) {
 		DPRINTF("Unable to initialise AIO state\n");
+                free_aio_state(bs);
 		goto fail;
 	}
 	init_fds(dd);
@@ -962,6 +1000,7 @@ int tdqcow_open (struct disk_driver *dd,
 	
 fail:
 	DPRINTF("QCOW Open failed\n");
+	free_aio_state(bs);
 	free(s->l1_table);
 	free(s->l2_cache);
 	free(s->cluster_cache);
@@ -1145,7 +1184,7 @@ int tdqcow_do_callbacks(struct disk_driv
         if (sid > MAX_IOFD) return 1;
 	
 	/* Non-blocking test for completed io. */
-        ret = io_getevents(prv->aio_ctx, 0, MAX_AIO_REQS, prv->aio_events,
+        ret = io_getevents(prv->aio_ctx, 0, prv->max_aio_reqs, prv->aio_events,
                            NULL);
 
         for (ep = prv->aio_events, i = ret; i-- > 0; ep++) {

[-- Attachment #3: Type: text/plain, Size: 138 bytes --]

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Re: [PATCH] Segments can span multiple clusters with tap:qcow

[Keir Fraser]

On 25/4/07 21:41, "Mark McLoughlin" <markmc@redhat.com> wrote:

> In blktap's qcow we need split up read/write requests if the requests
> span multiple clusters. However, with our MAX_AIO_REQUESTS define we
> assume that there is only ever a single aio request per tapdisk request
> and under heavy i/o we can run out of room causing us to cancel
> requests.
> 
> The attached patch dynamically allocates (based on cluster_bits) the
> various io request queues the driver maintains.

The current code allocates aio-request info for every segment in a request
ring (MAX_AIO_REQUESTS == BLK_RING_SIZE * MAX_SEGMENTS_PER_REQUEST). This
patch seems to take into account that each segment (part-of-page) can itself
be split into clusters, hence the page_size/cluster_size calculation, but
shouldn't this be multiplied by the existing MAX_AIO_REQUESTS? Otherwise you
provide only enough aio requests for one segment at a time, rather than a
request ring's worth of segments?

 -- Keir

Re: [PATCH] Segments can span multiple clusters with tap:qcow

[Mark McLoughlin]

[-- Attachment #1: Type: text/plain, Size: 1234 bytes --]

Hi Keir,

On Thu, 2007-04-26 at 10:09 +0100, Keir Fraser wrote:
> On 25/4/07 21:41, "Mark McLoughlin" <markmc@redhat.com> wrote:
> 
> > In blktap's qcow we need split up read/write requests if the requests
> > span multiple clusters. However, with our MAX_AIO_REQUESTS define we
> > assume that there is only ever a single aio request per tapdisk request
> > and under heavy i/o we can run out of room causing us to cancel
> > requests.
> > 
> > The attached patch dynamically allocates (based on cluster_bits) the
> > various io request queues the driver maintains.
> 
> The current code allocates aio-request info for every segment in a request
> ring (MAX_AIO_REQUESTS == BLK_RING_SIZE * MAX_SEGMENTS_PER_REQUEST). This
> patch seems to take into account that each segment (part-of-page) can itself
> be split into clusters, hence the page_size/cluster_size calculation, but
> shouldn't this be multiplied by the existing MAX_AIO_REQUESTS? Otherwise you
> provide only enough aio requests for one segment at a time, rather than a
> request ring's worth of segments?

	Absolutely, well spotted. I fixed that typo after testing, but
obviously forgot to run "quilt refresh" before sending ...

	Fixed version attached.

Thanks,
Mark.

[-- Attachment #2: block-qcow-multiple-aio-requests-per-segment.patch --]
[-- Type: text/x-patch, Size: 4932 bytes --]

diff -r 33e22185002a tools/blktap/drivers/block-qcow.c
--- a/tools/blktap/drivers/block-qcow.c	Wed Apr 25 13:50:20 2007 +0100
+++ b/tools/blktap/drivers/block-qcow.c	Wed Apr 25 21:32:37 2007 +0100
@@ -55,7 +55,6 @@
 
 /******AIO DEFINES******/
 #define REQUEST_ASYNC_FD 1
-#define MAX_AIO_REQS (MAX_REQUESTS * MAX_SEGMENTS_PER_REQ)
 
 struct pending_aio {
         td_callback_t cb;
@@ -146,18 +145,37 @@ struct tdqcow_state {
 	AES_KEY aes_encrypt_key;       /*AES key*/
 	AES_KEY aes_decrypt_key;       /*AES key*/
         /* libaio state */
-        io_context_t       aio_ctx;
-        struct iocb        iocb_list  [MAX_AIO_REQS];
-        struct iocb       *iocb_free  [MAX_AIO_REQS];
-        struct pending_aio pending_aio[MAX_AIO_REQS];
-        int                iocb_free_count;
-        struct iocb       *iocb_queue[MAX_AIO_REQS];
-        int                iocb_queued;
-        int                poll_fd;      /* NB: we require aio_poll support */
-        struct io_event    aio_events[MAX_AIO_REQS];
+        io_context_t        aio_ctx;
+        int                 max_aio_reqs;
+        struct iocb        *iocb_list;
+        struct iocb       **iocb_free;
+        struct pending_aio *pending_aio;
+        int                 iocb_free_count;
+        struct iocb       **iocb_queue;
+        int                 iocb_queued;
+        int                 poll_fd;      /* NB: we require aio_poll support */
+        struct io_event    *aio_events;
 };
 
 static int decompress_cluster(struct tdqcow_state *s, uint64_t cluster_offset);
+
+static void free_aio_state(struct td_state *bs)
+{
+	struct tdqcow_state *s = (struct tdqcow_state *)bs->private;
+
+        if (s->sector_lock)
+                free(s->sector_lock);
+        if (s->iocb_list)
+                free(s->iocb_list);
+        if (s->pending_aio)
+                free(s->pending_aio);
+        if (s->aio_events)
+                free(s->aio_events);
+        if (s->iocb_free)
+                free(s->iocb_free);
+        if (s->iocb_queue)
+                free(s->iocb_queue);
+}
 
 static int init_aio_state(struct disk_driver *dd)
 {
@@ -166,6 +184,12 @@ static int init_aio_state(struct disk_dr
 	struct tdqcow_state  *s = (struct tdqcow_state *)dd->private;
         long     ioidx;
 
+        s->iocb_list = NULL;
+        s->pending_aio = NULL;
+        s->aio_events = NULL;
+        s->iocb_free = NULL;
+        s->iocb_queue = NULL;
+
         /*Initialize Locking bitmap*/
 	s->sector_lock = calloc(1, bs->size);
 	
@@ -174,13 +198,26 @@ static int init_aio_state(struct disk_dr
 		goto fail;
 	}
 
+        /* A segment (i.e. a page) can span multiple clusters */
+        s->max_aio_reqs = ((getpagesize() / s->cluster_size) + 1) * MAX_SEGMENTS_PER_REQ * MAX_REQUESTS;
+
         /* Initialize AIO */
-        s->iocb_free_count = MAX_AIO_REQS;
+        s->iocb_free_count = s->max_aio_reqs;
         s->iocb_queued     = 0;
+
+        if (!(s->iocb_list = malloc(sizeof(struct iocb) * s->max_aio_reqs)) ||
+            !(s->pending_aio = malloc(sizeof(struct pending_aio) * s->max_aio_reqs)) ||
+            !(s->aio_events = malloc(sizeof(struct io_event) * s->max_aio_reqs)) ||
+            !(s->iocb_free = malloc(sizeof(struct iocb *) * s->max_aio_reqs)) ||
+            !(s->iocb_queue = malloc(sizeof(struct iocb *) * s->max_aio_reqs))) {
+                DPRINTF("Failed to allocate AIO structs (max_aio_reqs = %d)\n",
+                        s->max_aio_reqs);
+                goto fail;
+        }
 
         /*Signal kernel to create Poll FD for Asyc completion events*/
         s->aio_ctx = (io_context_t) REQUEST_ASYNC_FD;   
-        s->poll_fd = io_setup(MAX_AIO_REQS, &s->aio_ctx);
+        s->poll_fd = io_setup(s->max_aio_reqs, &s->aio_ctx);
 
 	if (s->poll_fd < 0) {
                 if (s->poll_fd == -EAGAIN) {
@@ -198,7 +235,7 @@ static int init_aio_state(struct disk_dr
 		goto fail;
 	}
 
-        for (i=0;i<MAX_AIO_REQS;i++)
+        for (i=0;i<s->max_aio_reqs;i++)
                 s->iocb_free[i] = &s->iocb_list[i];
 
         DPRINTF("AIO state initialised\n");
@@ -946,6 +983,7 @@ int tdqcow_open (struct disk_driver *dd,
  end_xenhdr:
 	if (init_aio_state(dd)!=0) {
 		DPRINTF("Unable to initialise AIO state\n");
+                free_aio_state(bs);
 		goto fail;
 	}
 	init_fds(dd);
@@ -962,6 +1000,7 @@ int tdqcow_open (struct disk_driver *dd,
 	
 fail:
 	DPRINTF("QCOW Open failed\n");
+	free_aio_state(bs);
 	free(s->l1_table);
 	free(s->l2_cache);
 	free(s->cluster_cache);
@@ -1145,7 +1184,7 @@ int tdqcow_do_callbacks(struct disk_driv
         if (sid > MAX_IOFD) return 1;
 	
 	/* Non-blocking test for completed io. */
-        ret = io_getevents(prv->aio_ctx, 0, MAX_AIO_REQS, prv->aio_events,
+        ret = io_getevents(prv->aio_ctx, 0, prv->max_aio_reqs, prv->aio_events,
                            NULL);
 
         for (ep = prv->aio_events, i = ret; i-- > 0; ep++) {

[-- Attachment #3: Type: text/plain, Size: 138 bytes --]

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Re: [PATCH] Segments can span multiple clusters with tap:qcow

[Keir Fraser]

On 26/4/07 10:18, "Mark McLoughlin" <markmc@redhat.com> wrote:

>> The current code allocates aio-request info for every segment in a request
>> ring (MAX_AIO_REQUESTS == BLK_RING_SIZE * MAX_SEGMENTS_PER_REQUEST). This
>> patch seems to take into account that each segment (part-of-page) can itself
>> be split into clusters, hence the page_size/cluster_size calculation, but
>> shouldn't this be multiplied by the existing MAX_AIO_REQUESTS? Otherwise you
>> provide only enough aio requests for one segment at a time, rather than a
>> request ring's worth of segments?
> 
> Absolutely, well spotted. I fixed that typo after testing, but
> obviously forgot to run "quilt refresh" before sending ...
> 
> Fixed version attached.

This one doesn't build (free_aio_state: line 164: structure has no member
named 'private'). Perhaps free_aio_state() should take a 'struct
disk_driver' rather than a 'struct td_state'?

 -- Keir

Re: [PATCH] Segments can span multiple clusters with tap:qcow

[Mark McLoughlin]

[-- Attachment #1: Type: text/plain, Size: 1082 bytes --]

On Thu, 2007-04-26 at 11:00 +0100, Keir Fraser wrote:
> On 26/4/07 10:18, "Mark McLoughlin" <markmc@redhat.com> wrote:
> 
> >> The current code allocates aio-request info for every segment in a request
> >> ring (MAX_AIO_REQUESTS == BLK_RING_SIZE * MAX_SEGMENTS_PER_REQUEST). This
> >> patch seems to take into account that each segment (part-of-page) can itself
> >> be split into clusters, hence the page_size/cluster_size calculation, but
> >> shouldn't this be multiplied by the existing MAX_AIO_REQUESTS? Otherwise you
> >> provide only enough aio requests for one segment at a time, rather than a
> >> request ring's worth of segments?
> > 
> > Absolutely, well spotted. I fixed that typo after testing, but
> > obviously forgot to run "quilt refresh" before sending ...
> > 
> > Fixed version attached.
> 
> This one doesn't build (free_aio_state: line 164: structure has no member
> named 'private'). Perhaps free_aio_state() should take a 'struct
> disk_driver' rather than a 'struct td_state'?

	Gah, merge error going from 3.0.4 to 3.0.5. This one builds.

Thanks,
Mark.

[-- Attachment #2: block-qcow-multiple-aio-requests-per-segment.patch --]
[-- Type: text/x-patch, Size: 4894 bytes --]

diff -r 33e22185002a tools/blktap/drivers/block-qcow.c
--- a/tools/blktap/drivers/block-qcow.c	Wed Apr 25 13:50:20 2007 +0100
+++ b/tools/blktap/drivers/block-qcow.c	Thu Apr 26 11:15:46 2007 +0100
@@ -55,7 +55,6 @@
 
 /******AIO DEFINES******/
 #define REQUEST_ASYNC_FD 1
-#define MAX_AIO_REQS (MAX_REQUESTS * MAX_SEGMENTS_PER_REQ)
 
 struct pending_aio {
         td_callback_t cb;
@@ -146,18 +145,37 @@ struct tdqcow_state {
 	AES_KEY aes_encrypt_key;       /*AES key*/
 	AES_KEY aes_decrypt_key;       /*AES key*/
         /* libaio state */
-        io_context_t       aio_ctx;
-        struct iocb        iocb_list  [MAX_AIO_REQS];
-        struct iocb       *iocb_free  [MAX_AIO_REQS];
-        struct pending_aio pending_aio[MAX_AIO_REQS];
-        int                iocb_free_count;
-        struct iocb       *iocb_queue[MAX_AIO_REQS];
-        int                iocb_queued;
-        int                poll_fd;      /* NB: we require aio_poll support */
-        struct io_event    aio_events[MAX_AIO_REQS];
+        io_context_t        aio_ctx;
+        int                 max_aio_reqs;
+        struct iocb        *iocb_list;
+        struct iocb       **iocb_free;
+        struct pending_aio *pending_aio;
+        int                 iocb_free_count;
+        struct iocb       **iocb_queue;
+        int                 iocb_queued;
+        int                 poll_fd;      /* NB: we require aio_poll support */
+        struct io_event    *aio_events;
 };
 
 static int decompress_cluster(struct tdqcow_state *s, uint64_t cluster_offset);
+
+static void free_aio_state(struct disk_driver *dd)
+{
+	struct tdqcow_state *s = (struct disk_driver *)dd->private;
+
+        if (s->sector_lock)
+                free(s->sector_lock);
+        if (s->iocb_list)
+                free(s->iocb_list);
+        if (s->pending_aio)
+                free(s->pending_aio);
+        if (s->aio_events)
+                free(s->aio_events);
+        if (s->iocb_free)
+                free(s->iocb_free);
+        if (s->iocb_queue)
+                free(s->iocb_queue);
+}
 
 static int init_aio_state(struct disk_driver *dd)
 {
@@ -166,6 +184,12 @@ static int init_aio_state(struct disk_dr
 	struct tdqcow_state  *s = (struct tdqcow_state *)dd->private;
         long     ioidx;
 
+        s->iocb_list = NULL;
+        s->pending_aio = NULL;
+        s->aio_events = NULL;
+        s->iocb_free = NULL;
+        s->iocb_queue = NULL;
+
         /*Initialize Locking bitmap*/
 	s->sector_lock = calloc(1, bs->size);
 	
@@ -174,13 +198,26 @@ static int init_aio_state(struct disk_dr
 		goto fail;
 	}
 
+        /* A segment (i.e. a page) can span multiple clusters */
+        s->max_aio_reqs = (getpagesize() / s->cluster_size) + 1;
+
         /* Initialize AIO */
-        s->iocb_free_count = MAX_AIO_REQS;
+        s->iocb_free_count = s->max_aio_reqs;
         s->iocb_queued     = 0;
+
+        if (!(s->iocb_list = malloc(sizeof(struct iocb) * s->max_aio_reqs)) ||
+            !(s->pending_aio = malloc(sizeof(struct pending_aio) * s->max_aio_reqs)) ||
+            !(s->aio_events = malloc(sizeof(struct io_event) * s->max_aio_reqs)) ||
+            !(s->iocb_free = malloc(sizeof(struct iocb *) * s->max_aio_reqs)) ||
+            !(s->iocb_queue = malloc(sizeof(struct iocb *) * s->max_aio_reqs))) {
+                DPRINTF("Failed to allocate AIO structs (max_aio_reqs = %d)\n",
+                        s->max_aio_reqs);
+                goto fail;
+        }
 
         /*Signal kernel to create Poll FD for Asyc completion events*/
         s->aio_ctx = (io_context_t) REQUEST_ASYNC_FD;   
-        s->poll_fd = io_setup(MAX_AIO_REQS, &s->aio_ctx);
+        s->poll_fd = io_setup(s->max_aio_reqs, &s->aio_ctx);
 
 	if (s->poll_fd < 0) {
                 if (s->poll_fd == -EAGAIN) {
@@ -198,7 +235,7 @@ static int init_aio_state(struct disk_dr
 		goto fail;
 	}
 
-        for (i=0;i<MAX_AIO_REQS;i++)
+        for (i=0;i<s->max_aio_reqs;i++)
                 s->iocb_free[i] = &s->iocb_list[i];
 
         DPRINTF("AIO state initialised\n");
@@ -946,6 +983,7 @@ int tdqcow_open (struct disk_driver *dd,
  end_xenhdr:
 	if (init_aio_state(dd)!=0) {
 		DPRINTF("Unable to initialise AIO state\n");
+                free_aio_state(dd);
 		goto fail;
 	}
 	init_fds(dd);
@@ -962,6 +1000,7 @@ int tdqcow_open (struct disk_driver *dd,
 	
 fail:
 	DPRINTF("QCOW Open failed\n");
+	free_aio_state(dd);
 	free(s->l1_table);
 	free(s->l2_cache);
 	free(s->cluster_cache);
@@ -1145,7 +1184,7 @@ int tdqcow_do_callbacks(struct disk_driv
         if (sid > MAX_IOFD) return 1;
 	
 	/* Non-blocking test for completed io. */
-        ret = io_getevents(prv->aio_ctx, 0, MAX_AIO_REQS, prv->aio_events,
+        ret = io_getevents(prv->aio_ctx, 0, prv->max_aio_reqs, prv->aio_events,
                            NULL);
 
         for (ep = prv->aio_events, i = ret; i-- > 0; ep++) {

[-- Attachment #3: Type: text/plain, Size: 138 bytes --]

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RE: [PATCH] Segments can span multiple clusters withtap:qcow

[Jake Wires]

Hi,

This patch is back to only allocating enough requests for one segment:

+        /* A segment (i.e. a page) can span multiple clusters */
+        s->max_aio_reqs = (getpagesize() / s->cluster_size) + 1;

In fact, this code allocates exactly two AIO requests for QCoW images
created by qcow-create, which have a default cluster size of 4K.

For a while now, tapdisk has supported EBUSY -- that is, if a plugin
returns -EBUSY to tapdisk, tapdisk will put the last segment back on its
queue and wait until the plugin has made progress before reissuing the
request.  Thus users should not observe an error when QCoW runs out of
AIO requests.  This is attested by the fact that even with only 2 AIO
requests allocated, QCoW block devices can handle a heavy load: I just
mkfs'ed and copied a 1GB file to a QCoW image with no problem --
although it took quite a long while to do so, since only two segments
were served at a time ;).

If you were observing errors while writing to QCoW devices, I'd like to
know how you were causing them -- we may need to make some other changes
to fix them.  However, I'm not convinced that this patch is necessary.

Thanks,
Jake

> -----Original Message-----
> From: xen-devel-bounces@lists.xensource.com [mailto:xen-devel-
> bounces@lists.xensource.com] On Behalf Of Mark McLoughlin
> Sent: Thursday, April 26, 2007 3:21 AM
> To: Keir Fraser
> Cc: xen-devel
> Subject: Re: [Xen-devel] [PATCH] Segments can span multiple clusters
> withtap:qcow
> 
> On Thu, 2007-04-26 at 11:00 +0100, Keir Fraser wrote:
> > On 26/4/07 10:18, "Mark McLoughlin" <markmc@redhat.com> wrote:
> >
> > >> The current code allocates aio-request info for every segment in
a
> request
> > >> ring (MAX_AIO_REQUESTS == BLK_RING_SIZE *
MAX_SEGMENTS_PER_REQUEST).
> This
> > >> patch seems to take into account that each segment (part-of-page)
can
> itself
> > >> be split into clusters, hence the page_size/cluster_size
calculation,
> but
> > >> shouldn't this be multiplied by the existing MAX_AIO_REQUESTS?
> Otherwise you
> > >> provide only enough aio requests for one segment at a time,
rather
> than a
> > >> request ring's worth of segments?
> > >
> > > Absolutely, well spotted. I fixed that typo after testing, but
> > > obviously forgot to run "quilt refresh" before sending ...
> > >
> > > Fixed version attached.
> >
> > This one doesn't build (free_aio_state: line 164: structure has no
> member
> > named 'private'). Perhaps free_aio_state() should take a 'struct
> > disk_driver' rather than a 'struct td_state'?
> 
> 	Gah, merge error going from 3.0.4 to 3.0.5. This one builds.
> 
> Thanks,
> Mark.

Re: [PATCH] Segments can span multiple clusters withtap:qcow

[Keir Fraser]

On 3/5/07 02:06, "Jake Wires" <Jake.Wires@xensource.com> wrote:

> This patch is back to only allocating enough requests for one segment:
> 
> +        /* A segment (i.e. a page) can span multiple clusters */
> +        s->max_aio_reqs = (getpagesize() / s->cluster_size) + 1;
> 
> In fact, this code allocates exactly two AIO requests for QCoW images
> created by qcow-create, which have a default cluster size of 4K.

What shall we do -- revert the whole patch or fix this line?

 -- Keir

Re: [PATCH] Segments can span multiple clusters withtap:qcow

[Mark McLoughlin]

On Thu, 2007-05-03 at 18:40 +0100, Keir Fraser wrote:
> On 3/5/07 02:06, "Jake Wires" <Jake.Wires@xensource.com> wrote:
> 
> > This patch is back to only allocating enough requests for one segment:
> > 
> > +        /* A segment (i.e. a page) can span multiple clusters */
> > +        s->max_aio_reqs = (getpagesize() / s->cluster_size) + 1;
> > 
> > In fact, this code allocates exactly two AIO requests for QCoW images
> > created by qcow-create, which have a default cluster size of 4K.
> 
> What shall we do -- revert the whole patch or fix this line?

	Goodness, words fail me. In all the confusion I created, that fix got
lost again. It should be:

+        s->max_aio_reqs = ((getpagesize() / s->cluster_size) + 1) * MAX_SEGMENTS_PER_REQ * MAX_REQUESTS;

Thanks,
Mark.

RE: [PATCH] Segments can span multiple clusters withtap:qcow

[Mark McLoughlin]

On Wed, 2007-05-02 at 18:06 -0700, Jake Wires wrote:
> Hi,
> 
> This patch is back to only allocating enough requests for one segment:
> 
> +        /* A segment (i.e. a page) can span multiple clusters */
> +        s->max_aio_reqs = (getpagesize() / s->cluster_size) + 1;
> 
> In fact, this code allocates exactly two AIO requests for QCoW images
> created by qcow-create, which have a default cluster size of 4K.
> 
> For a while now, tapdisk has supported EBUSY -- that is, if a plugin
> returns -EBUSY to tapdisk, tapdisk will put the last segment back on its
> queue and wait until the plugin has made progress before reissuing the
> request.

	Yep.

>   Thus users should not observe an error when QCoW runs out of
> AIO requests.  This is attested by the fact that even with only 2 AIO
> requests allocated, QCoW block devices can handle a heavy load: I just
> mkfs'ed and copied a 1GB file to a QCoW image with no problem --
> although it took quite a long while to do so, since only two segments
> were served at a time ;).

	Uggh.

> If you were observing errors while writing to QCoW devices, I'd like to
> know how you were causing them -- we may need to make some other changes
> to fix them.  However, I'm not convinced that this patch is necessary.

	I was seeing errors with the pre-EBUSY code, but I figured we would
still prefer to allocate the max number of segments.

	Point taken that it's not critical, though. At this point, reverting
until after 3.1.0 wouldn't be crazy.

Thanks,
Mark.