δΊ 2013-8-27 22:39, Stefan Hajnoczi ει: > It can be useful to run an AioContext from a thread which normally does > not "own" the AioContext. For example, request draining can be > implemented by acquiring the AioContext and looping aio_poll() until all > requests have been completed. > > The following pattern should work: > > /* Event loop thread */ > while (running) { > aio_context_acquire(ctx); > aio_poll(ctx, true); > aio_context_release(ctx); > } > > /* Another thread */ > aio_context_acquire(ctx); > bdrv_read(bs, 0x1000, buf, 1); > aio_context_release(ctx); > > This patch implements aio_context_acquire() and aio_context_release(). > Note that existing aio_poll() callers do not need to worry about > acquiring and releasing - it is only needed when multiple threads will > call aio_poll() on the same AioContext. > > Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com> > ---
After a chat with Stefan on IRC, To enable block layer usage by multiple thread, there are two potential program models. Thanks for Stefan's analysis, I think it would be helpful to share the info as following, pls correct me if my understanding is not right: The models: 1) context per request model: aio_context_acquire(ctx); bds_acquire(bds); bdrv_aio_read(AioContext *ctx, BlockDriverStates *bds, ...); bds_release(bds); aio_context_release(ctx); 2) context per BDS model: BlockDriverState *bds = bdrv_new(AioContext *ctx); /* or another API bind AioContext */ aio_context_acquire(ctx); bdrv_aio_read(BlockDriverStates *bds, ...); aio_context_release(ctx); The difference: context per request model in 1): AioContext c0 AioContext c1 /|\ /|\ |----------------| | | ------------------- /|\ | | | BDS b0 BDS b1.. /|\ | ------------- /|\ /|\ | | request request from thread from thread t0 who t1 who acquired c0 acquired c1 context per BDS model in 2): AioContext c0 AioContext c1 /|\ | | | | | BDS b0 BDS b1.. /|\ | | request from thread t0 who acquired c0 (t1's request can't submitted at this time) If BDS is considered as front end used to submit task, AioContext is considered as a back end used to process task, whether to bind BDS with AioContext, determine whether the request for one BDS, can be submitted in front end, processed in the back end, in parallel. Generally speaking 1) will gain more parallel capability, it enable multiple thread usage at BDS level, but requires more code inside block layer, for sync and series/parallel request converting, so we are heading to 2), request will be submitted. Interesting thing is that, it can still enable multiple thread usage in AioContext level: AioContext c0 AioContext c1 /|\ /|\ | | | | BDS b0 BDS b1 /|\ /|\ | | | | request request from thread from thread t0 who t1 who acquired c0 acquired c1 So later dataplane thread will becomes another user who create a AioContext to do jobs in parallel. -- Best Regards Wenchao Xia