Am 25.02.2016 um 10:06 hat Pavel Dovgalyuk geschrieben: > > From: Kevin Wolf [mailto:kw...@redhat.com] > > > > Coroutines aren't randomly assigned to threads, but threads actively > > > > enter coroutines. To my knowledge this happens only when starting a > > > > request (either vcpu or I/O thread; consistent per device) or by a > > > > callback when some event happens (only I/O thread). I can't see any > > > > non-determinism here. > > > > > > Behavior of coroutines looks strange for me. > > > Consider the code below (co_readv function of the replay driver). > > > In record mode it somehow changes the thread it assigned to. > > > Code in point A is executed in CPU thread and code in point B - in some > > > other thread. > > > May this happen because this coroutine yields somewhere and its execution > > > is restored > > > by aio_poll, which is called from iothread? > > > In this case event finishing callback cannot be executed deterministically > > > (always in CPU thread or always in IO thread). > > > > > > static int coroutine_fn blkreplay_co_readv(BlockDriverState *bs, > > > int64_t sector_num, int nb_sectors, QEMUIOVector *qiov) > > > { > > > BDRVBlkreplayState *s = bs->opaque; > > > uint32_t reqid = request_id++; > > > Request *req; > > > // A > > > bdrv_co_readv(bs->file->bs, sector_num, nb_sectors, qiov); > > > > > > if (replay_mode == REPLAY_MODE_RECORD) { > > > replay_save_block_event(reqid); > > > } else { > > > assert(replay_mode == REPLAY_MODE_PLAY); > > > if (reqid == current_request) { > > > current_finished = true; > > > } else { > > > req = block_request_insert(reqid, bs, qemu_coroutine_self()); > > > qemu_coroutine_yield(); > > > block_request_remove(req); > > > } > > > } > > > // B > > > return 0; > > > } > > > > Yes, I guess this can happen. As I described above, the coroutine can be > > entered from a vcpu thread initially. After yielding for the first time, > > it is resumed from the I/O thread. So if there are paths where the > > coroutine never yields, the coroutine completes in the original vcpu > > thread. (It's not the common case that bdrv_co_readv() doesn't yield, > > but it happens e.g. with unallocated sectors in qcow2.) > > > > If this is a problem for you, you need to force the coroutine into the > > I/O thread. You can do that by scheduling a BH, then yield, and then let > > the BH reenter the coroutine. > > Thanks, this approach seems to work. I got rid of replay_run_block_event, > because BH basically does the same job. > > There is one problem with flush event - callbacks for flush are called for > all layers and I couldn't synchronize them correctly yet. > I'll probably have to add new callback to block driver, which handles > flush request for the whole stack of the drivers.
Flushes should be treated more or less the same a writes, I think. Kevin
