Re: [PATCH v3 37/42] hpsa: use block layer tag for command allocation

Tomas Henzl
2015-03-26T12:48:26Z

On 03/25/2015 07:33 PM, Webb Scales wrote:
> Tomas,
>
> You are correct that the previous approach of using find_next_zero_bit()
> with a persistent offset is more run-time efficient in the worst case;
> however, given that "normal" operation doesn't call this allocation
> routine, and given that, when this routine is called, the bit mask being
> searched only has about 16 bits in it, I opted for simplicity over
> efficiency -- that is, I doubt that the difference in efficiency is
> discernible, while getting rid of the last_allocation field is a
> worthwhile savings in both memory use and code.

My comment is not about efficiency, I believe that when you measure it you wont be
able to measure any significant difference.
But if this '(unlikely(refcount > 1))' is true for let's say the first entry in the bitfield
this and any other command submitted later will not pass the cmd-alloc until the command that
caused '(unlikely(refcount > 1))' to be true is resolved. That might cause unexpected
behavior.

> Regarding your earlier comment on the refcount variable, I believe that
> it was handy for debugging purposes. The code has undergone numerous
> revisions, and the variable certainly could now be removed from the
> source per your suggestion. (Of course, the compiler is already
> removing it, I'm sure. ;-) )

Not sure if the compiler is able to switch from 'atomic_inc_return' to 'atomic_inc' :) though.
It is not important. (I'd not comment on this without the other cmd_alloc inaccuracy)

tomash

>
>
> Webb
>
>
>
> -----Original Message-----
> From: Tomas Henzl [mailto:thenzl@redhat.com]
> Sent: Monday, March 23, 2015 11:58 AM
> To: Don Brace; Scott Teel; Kevin Barnett; james.bottomley@parallels.com; hch@infradead.org; Justin Lindley; brace
> Cc: linux-scsi@vger.kernel.org
> Subject: Re: [PATCH v3 37/42] hpsa: use block layer tag for command allocation
>
> On 03/17/2015 09:06 PM, Don Brace wrote:
>
>> From: Webb Scales <webbnh@hp.com>
>>
>> Rework slave allocation:
>> - separate the tagging support setup from the hostdata setup
>> - make the hostdata setup act consistently when the lookup fails
>> - make the hostdata setup act consistently when the device is not added
>> - set up the queue depth consistently across these scenarios
>> - if the block layer mq support is not available, explicitly enable and
>> activate the SCSI layer tcq support (and do this at allocation-time so
>> that the tags will be available for INQUIRY commands)
>>
>> Tweak slave configuration so that devices which are masked are also
>> not attached.
>>
>> Reviewed-by: Scott Teel <scott.teel@pmcs.com>
>> Reviewed-by: Kevin Barnett <kevin.barnett@pmcs.com>
>> Signed-off-by: Webb Scales <webbnh@hp.com>
>> Signed-off-by: Don Brace <don.brace@pmcs.com>
>> ---
>> drivers/scsi/hpsa.c | 153 +++++++++++++++++++++++++++++++++++++++++----------
>> drivers/scsi/hpsa.h | 1
>> 2 files changed, 123 insertions(+), 31 deletions(-)
>>
>> diff --git a/drivers/scsi/hpsa.c b/drivers/scsi/hpsa.c
>> index 34c178c..4e34a62 100644
>> --- a/drivers/scsi/hpsa.c
>> +++ b/drivers/scsi/hpsa.c
>> @@ -44,6 +44,7 @@
>> #include <scsi/scsi_host.h>
>> #include <scsi/scsi_tcq.h>
>> #include <scsi/scsi_eh.h>
>> +#include <scsi/scsi_dbg.h>
>> #include <linux/cciss_ioctl.h>
>> #include <linux/string.h>
>> #include <linux/bitmap.h>
>> @@ -212,6 +213,9 @@ static int hpsa_compat_ioctl(struct scsi_device *dev, int cmd,
>>
>> static void cmd_free(struct ctlr_info *h, struct CommandList *c);
>> static struct CommandList *cmd_alloc(struct ctlr_info *h);
>> +static void cmd_tagged_free(struct ctlr_info *h, struct CommandList *c);
>> +static struct CommandList *cmd_tagged_alloc(struct ctlr_info *h,
>> + struct scsi_cmnd *scmd);
>> static int fill_cmd(struct CommandList *c, u8 cmd, struct ctlr_info *h,
>> void *buff, size_t size, u16 page_code, unsigned char *scsi3addr,
>> int cmd_type);
>> @@ -2047,11 +2051,17 @@ static void hpsa_cmd_resolve_events(struct ctlr_info *h,
>> }
>> }
>>
>> +static void hpsa_cmd_resolve_and_free(struct ctlr_info *h,
>> + struct CommandList *c)
>> +{
>> + hpsa_cmd_resolve_events(h, c);
>> + cmd_tagged_free(h, c);
>> +}
>> +
>> static void hpsa_cmd_free_and_done(struct ctlr_info *h,
>> struct CommandList *c, struct scsi_cmnd *cmd)
>> {
>> - hpsa_cmd_resolve_events(h, c);
>> - cmd_free(h, c);
>> + hpsa_cmd_resolve_and_free(h, c);
>> cmd->scsi_done(cmd);
>> }
>>
>> @@ -2072,8 +2082,7 @@ static void hpsa_cmd_abort_and_free(struct ctlr_info *h, struct CommandList *c,
>> hpsa_set_scsi_cmd_aborted(cmd);
>> dev_warn(&h->pdev->dev, "CDB %16phN was aborted with status 0x%x\n",
>> c->Request.CDB, c->err_info->ScsiStatus);
>> - hpsa_cmd_resolve_events(h, c);
>> - cmd_free(h, c); /* FIX-ME: change to cmd_tagged_free(h, c) */
>> + hpsa_cmd_resolve_and_free(h, c);
>> }
>>
>> static void process_ioaccel2_completion(struct ctlr_info *h,
>> @@ -4535,7 +4544,7 @@ static int hpsa_ciss_submit(struct ctlr_info *h,
>> }
>>
>> if (hpsa_scatter_gather(h, c, cmd) < 0) { /* Fill SG list */
>> - cmd_free(h, c);
>> + hpsa_cmd_resolve_and_free(h, c);
>> return SCSI_MLQUEUE_HOST_BUSY;
>> }
>> enqueue_cmd_and_start_io(h, c);
>> @@ -4581,6 +4590,8 @@ static inline void hpsa_cmd_partial_init(struct ctlr_info *h, int index,
>> {
>> dma_addr_t cmd_dma_handle = h->cmd_pool_dhandle + index * sizeof(*c);
>>
>> + BUG_ON(c->cmdindex != index);
>> +
>> memset(c->Request.CDB, 0, sizeof(c->Request.CDB));
>> memset(c->err_info, 0, sizeof(*c->err_info));
>> c->busaddr = (u32) cmd_dma_handle;
>> @@ -4675,27 +4686,24 @@ static int hpsa_scsi_queue_command(struct Scsi_Host *sh, struct scsi_cmnd *cmd)
>>
>> /* Get the ptr to our adapter structure out of cmd->host. */
>> h = sdev_to_hba(cmd->device);
>> +
>> + BUG_ON(cmd->request->tag < 0);
>> +
>> dev = cmd->device->hostdata;
>> if (!dev) {
>> cmd->result = DID_NO_CONNECT << 16;
>> cmd->scsi_done(cmd);
>> return 0;
>> }
>> - memcpy(scsi3addr, dev->scsi3addr, sizeof(scsi3addr));
>>
>> - if (unlikely(lockup_detected(h))) {
>> - cmd->result = DID_NO_CONNECT << 16;
>> - cmd->scsi_done(cmd);
>> - return 0;
>> - }
>> - c = cmd_alloc(h);
>> + memcpy(scsi3addr, dev->scsi3addr, sizeof(scsi3addr));
>>
>> if (unlikely(lockup_detected(h))) {
>> cmd->result = DID_NO_CONNECT << 16;
>> - cmd_free(h, c);
>> cmd->scsi_done(cmd);
>> return 0;
>> }
>> + c = cmd_tagged_alloc(h, cmd);
>>
>> /*
>> * Call alternate submit routine for I/O accelerated commands.
>> @@ -4708,7 +4716,7 @@ static int hpsa_scsi_queue_command(struct Scsi_Host *sh, struct scsi_cmnd *cmd)
>> if (rc == 0)
>> return 0;
>> if (rc == SCSI_MLQUEUE_HOST_BUSY) {
>> - cmd_free(h, c);
>> + hpsa_cmd_resolve_and_free(h, c);
>> return SCSI_MLQUEUE_HOST_BUSY;
>> }
>> }
>> @@ -4822,15 +4830,23 @@ static int hpsa_register_scsi(struct ctlr_info *h)
>> sh->hostdata[0] = (unsigned long) h;
>> sh->irq = h->intr[h->intr_mode];
>> sh->unique_id = sh->irq;
>> + error = scsi_init_shared_tag_map(sh, sh->can_queue);
>> + if (error) {
>> + dev_err(&h->pdev->dev,
>> + "%s: scsi_init_shared_tag_map failed for controller %d\n",
>> + __func__, h->ctlr);
>> + goto fail_host_put;
>> + }
>> error = scsi_add_host(sh, &h->pdev->dev);
>> - if (error)
>> + if (error) {
>> + dev_err(&h->pdev->dev, "%s: scsi_add_host failed for controller %d\n",
>> + __func__, h->ctlr);
>> goto fail_host_put;
>> + }
>> scsi_scan_host(sh);
>> return 0;
>>
>> fail_host_put:
>> - dev_err(&h->pdev->dev, "%s: scsi_add_host"
>> - " failed for controller %d\n", __func__, h->ctlr);
>> scsi_host_put(sh);
>> return error;
>> fail:
>> @@ -4840,6 +4856,23 @@ static int hpsa_register_scsi(struct ctlr_info *h)
>> }
>>
>> /*
>> + * The block layer has already gone to the trouble of picking out a unique,
>> + * small-integer tag for this request. We use an offset from that value as
>> + * an index to select our command block. (The offset allows us to reserve the
>> + * low-numbered entries for our own uses.)
>> + */
>> +static int hpsa_get_cmd_index(struct scsi_cmnd *scmd)
>> +{
>> + int idx = scmd->request->tag;
>> +
>> + if (idx < 0)
>> + return idx;
>> +
>> + /* Offset to leave space for internal cmds. */
>> + return idx += HPSA_NRESERVED_CMDS;
>> +}
>> +
>> +/*
>> * Send a TEST_UNIT_READY command to the specified LUN using the specified
>> * reply queue; returns zero if the unit is ready, and non-zero otherwise.
>> */
>> @@ -4979,18 +5012,18 @@ static int hpsa_eh_device_reset_handler(struct scsi_cmnd *scsicmd)
>> /* if controller locked up, we can guarantee command won't complete */
>> if (lockup_detected(h)) {
>> dev_warn(&h->pdev->dev,
>> - "scsi %d:%d:%d:%d RESET FAILED, lockup detected\n",
>> - h->scsi_host->host_no, dev->bus, dev->target,
>> - dev->lun);
>> + "scsi %d:%d:%d:%u cmd %d RESET FAILED, lockup detected\n",
>> + h->scsi_host->host_no, dev->bus, dev->target, dev->lun,
>> + hpsa_get_cmd_index(scsicmd));
>> return FAILED;
>> }
>>
>> /* this reset request might be the result of a lockup; check */
>> if (detect_controller_lockup(h)) {
>> dev_warn(&h->pdev->dev,
>> - "scsi %d:%d:%d:%d RESET FAILED, new lockup detected\n",
>> + "scsi %d:%d:%d:%u cmd %d RESET FAILED, new lockup detected\n",
>> h->scsi_host->host_no, dev->bus, dev->target,
>> - dev->lun);
>> + dev->lun, hpsa_get_cmd_index(scsicmd));
>> return FAILED;
>> }
>>
>> @@ -5442,6 +5475,59 @@ static int hpsa_eh_abort_handler(struct scsi_cmnd *sc)
>> }
>>
>> /*
>> + * For operations with an associated SCSI command, a command block is allocated
>> + * at init, and managed by cmd_tagged_alloc() and cmd_tagged_free() using the
>> + * block request tag as an index into a table of entries. cmd_tagged_free() is
>> + * the complement, although cmd_free() may be called instead.
>> + */
>> +static struct CommandList *cmd_tagged_alloc(struct ctlr_info *h,
>> + struct scsi_cmnd *scmd)
>> +{
>> + int idx = hpsa_get_cmd_index(scmd);
>> + struct CommandList *c = h->cmd_pool + idx;
>> + int refcount = 0;
>> +
>> + if (idx < HPSA_NRESERVED_CMDS || idx >= h->nr_cmds) {
>> + dev_err(&h->pdev->dev, "Bad block tag: %d not in [%d..%d]\n",
>> + idx, HPSA_NRESERVED_CMDS, h->nr_cmds - 1);
>> + /* The index value comes from the block layer, so if it's out of
>> + * bounds, it's probably not our bug.
>> + */
>> + BUG();
>> + }
>> +
>> + refcount = atomic_inc_return(&c->refcount);
> refcount is never used, use atomic_inc(&c->refcount); instead?
>
>> + if (unlikely(!hpsa_is_cmd_idle(c))) {
>> + /*
>> + * We expect that the SCSI layer will hand us a unique tag
>> + * value. Thus, there should never be a collision here between
>> + * two requests...because if the selected command isn't idle
>> + * then someone is going to be very disappointed.
>> + */
>> + dev_err(&h->pdev->dev,
>> + "tag collision (tag=%d) in cmd_tagged_alloc().\n",
>> + idx);
>> + if (c->scsi_cmd != NULL)
>> + scsi_print_command(c->scsi_cmd);
>> + scsi_print_command(scmd);
>> + }
>> +
>> + hpsa_cmd_partial_init(h, idx, c);
>> + return c;
>> +}
>> +
>> +static void cmd_tagged_free(struct ctlr_info *h, struct CommandList *c)
>> +{
>> + /*
>> + * Release our reference to the block. We don't need to do anything
>> + * else to free it, because it is accessed by index. (There's no point
>> + * in checking the result of the decrement, since we cannot guarantee
>> + * that there isn't a concurrent abort which is also accessing it.)
>> + */
>> + (void)atomic_dec(&c->refcount);
>> +}
>> +
>> +/*
>> * For operations that cannot sleep, a command block is allocated at init,
>> * and managed by cmd_alloc() and cmd_free() using a simple bitmap to track
>> * which ones are free or in use. Lock must be held when calling this.
>> @@ -5454,7 +5540,6 @@ static struct CommandList *cmd_alloc(struct ctlr_info *h)
>> {
>> struct CommandList *c;
>> int refcount, i;
>> - unsigned long offset;
>>
>> /*
>> * There is some *extremely* small but non-zero chance that that
>> @@ -5466,31 +5551,39 @@ static struct CommandList *cmd_alloc(struct ctlr_info *h)
>> * very unlucky thread might be starved anyway, never able to
>> * beat the other threads. In reality, this happens so
>> * infrequently as to be indistinguishable from never.
>> + *
>> + * Note that we start allocating commands before the SCSI host structure
>> + * is initialized. Since the search starts at bit zero, this
>> + * all works, since we have at least one command structure available;
>> + * however, it means that the structures with the low indexes have to be
>> + * reserved for driver-initiated requests, while requests from the block
>> + * layer will use the higher indexes.
>> */
>>
>> - offset = h->last_allocation; /* benignly racy */
>> for (;;) {
>> - i = find_next_zero_bit(h->cmd_pool_bits, h->nr_cmds, offset);
>> - if (unlikely(i == h->nr_cmds)) {
>> - offset = 0;
>> + i = find_first_zero_bit(h->cmd_pool_bits, HPSA_NRESERVED_CMDS);
>> + if (unlikely(i >= HPSA_NRESERVED_CMDS))
>> continue;
>> - }
>> c = h->cmd_pool + i;
>> refcount = atomic_inc_return(&c->refcount);
>> if (unlikely(refcount > 1)) {
>> cmd_free(h, c); /* already in use */
>> - offset = (i + 1) % h->nr_cmds;
> Hi Don,
> when this happens - a command has its bitfield flag cleared and, but it's taken - refcount is > 1
> it will be so likely for next several thousands of tests in this function until the it is freed.
> When it is the first bit in the bitfield it will block all following commands sent to the card for that time.
> The previous variant 'find_next_zero_bit + offset = (i + 1) % h->nr_cmds' seems to handle this better.
> Cheers, Tomas
>
>> continue;
>> }
>> set_bit(i & (BITS_PER_LONG - 1),
>> h->cmd_pool_bits + (i / BITS_PER_LONG));
>> break; /* it's ours now. */
>> }
>> - h->last_allocation = i; /* benignly racy */
>> hpsa_cmd_partial_init(h, i, c);
>> return c;
>> }
>>
>> +/*
>> + * This is the complementary operation to cmd_alloc(). Note, however, in some
>> + * corner cases it may also be used to free blocks allocated by
>> + * cmd_tagged_alloc() in which case the ref-count decrement does the trick and
>> + * the clear-bit is harmless.
>> + */
>> static void cmd_free(struct ctlr_info *h, struct CommandList *c)
>> {
>> if (atomic_dec_and_test(&c->refcount)) {
>> diff --git a/drivers/scsi/hpsa.h b/drivers/scsi/hpsa.h
>> index 3ec8934..2536b67 100644
>> --- a/drivers/scsi/hpsa.h
>> +++ b/drivers/scsi/hpsa.h
>> @@ -141,7 +141,6 @@ struct ctlr_info {
>> struct CfgTable __iomem *cfgtable;
>> int interrupts_enabled;
>> int max_commands;
>> - int last_allocation;
>> atomic_t commands_outstanding;
>> # define PERF_MODE_INT 0
>> # define DOORBELL_INT 1
>>
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