Re: [Qemu-devel] [PATCH] block: Let bdrv_drain_all() to call aio_poll() for each AioContext

[Alexander Yarygin <yarygin@linux.vnet.ibm.com>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 13/05/2015 18:34, Alexander Yarygin wrote:
>> Ah, right. We need second loop, something like this:
>> 
>> @@ -2030,20 +2033,33 @@ void bdrv_drain(BlockDriverState *bs)
>>  void bdrv_drain_all(void)
>>  {
>>      /* Always run first iteration so any pending completion BHs run */
>> -    bool busy = true;
>> +    bool busy = true, pending = false;
>>      BlockDriverState *bs;
>> +    GList *aio_ctxs = NULL, *ctx;
>> +    AioContext *aio_context;
>> 
>>      while (busy) {
>>          busy = false;
>> 
>>          QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
>> -            AioContext *aio_context = bdrv_get_aio_context(bs);
>> +            aio_context = bdrv_get_aio_context(bs);
>> 
>>              aio_context_acquire(aio_context);
>>              busy |= bdrv_drain_one(bs);
>>              aio_context_release(aio_context);
>> +            if (!aio_ctxs || !g_list_find(aio_ctxs, aio_context))
>> +                aio_ctxs = g_list_append(aio_ctxs, aio_context);
>> +        }
>> +        pending = busy;
>> +
>> +        for (ctx = aio_ctxs; ctx != NULL; ctx = ctx->next) {
>> +            aio_context = ctx->data;
>> +            aio_context_acquire(aio_context);
>> +            busy |= aio_poll(aio_context, pending);
>> +            aio_context_release(aio_context);
>>          }
>>      }
>> +    g_list_free(aio_ctxs);
>>  }
>> 
>> That looks quite ugly for me and breaks consistence of bdrv_drain_one()
>> since it doesn't call aio_poll() anymore...
>
> It's not ugly.  After your patch bdrv_drain_one doesn't call aio_poll,
> while bdrv_drain and bdrv_drain_all call bdrv_drain_one + aio_poll.  All
> callers of bdrv_drain_one are consistent.
>
> Perhaps you can rename bdrv_drain_one to bdrv_flush_io_queue (inlining
> the existing bdrv_flush_io_queue into it)?  That would work very well
> for me.
>
> Paolo

Hmm, bdrv_flush_io_queue() is public, but has no users. How about
different name, maybe something like "bdrv_drain_requests_one" or so?

Otherwise here is a patch related to renaming to bdrv_flush_io_queue()
below. If it's ok, I will respin the whole patch.

Thanks.

--- a/block.c
+++ b/block.c
@@ -1987,11 +1987,17 @@ static bool bdrv_requests_pending(BlockDriverState *bs)
     return false;
 }
 
-static bool bdrv_drain_one(BlockDriverState *bs)
+static bool bdrv_flush_io_queue(BlockDriverState *bs)
 {
     bool bs_busy;
+    BlockDriver *drv = bs->drv;
+
+    if (drv && drv->bdrv_flush_io_queue) {
+        drv->bdrv_flush_io_queue(bs);
+    } else if (bs->file) {
+        bdrv_flush_io_queue(bs->file);
+    }
 
-    bdrv_flush_io_queue(bs);
     bdrv_start_throttled_reqs(bs);
     bs_busy = bdrv_requests_pending(bs);
     return bs_busy;
@@ -2013,7 +2019,7 @@ void bdrv_drain(BlockDriverState *bs)
 
     while (busy) {
         /* Keep iterating */
-        busy = bdrv_drain_one(bs);
+        busy = bdrv_flush_io_queue(bs);
         busy |= aio_poll(bdrv_get_aio_context(bs), busy);
     }
 }
@@ -2044,7 +2050,7 @@ void bdrv_drain_all(void)
             AioContext *aio_context = bdrv_get_aio_context(bs);
 
             aio_context_acquire(aio_context);
-            busy |= bdrv_drain_one(bs);
+            busy |= bdrv_flush_io_queue(bs);
             if (!aio_ctxs || !g_slist_find(aio_ctxs, aio_context)) {
                 busy |= aio_poll(aio_context, busy);
                 aio_ctxs = g_slist_prepend(aio_ctxs, aio_context);
@@ -6088,16 +6094,6 @@ void bdrv_io_unplug(BlockDriverState *bs)
     }
 }
 
-void bdrv_flush_io_queue(BlockDriverState *bs)
-{
-    BlockDriver *drv = bs->drv;
-    if (drv && drv->bdrv_flush_io_queue) {
-        drv->bdrv_flush_io_queue(bs);
-    } else if (bs->file) {
-        bdrv_flush_io_queue(bs->file);
-    }
-}
-
 static bool append_open_options(QDict *d, BlockDriverState *bs)
 {
     const QDictEntry *entry;
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -565,7 +565,6 @@ int bdrv_probe_geometry(BlockDriverState *bs, HDGeometry *geo);
 
 void bdrv_io_plug(BlockDriverState *bs);
 void bdrv_io_unplug(BlockDriverState *bs);
-void bdrv_flush_io_queue(BlockDriverState *bs);
 
 BlockAcctStats *bdrv_get_stats(BlockDriverState *bs);