[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH 00/16] aio_context_acquire/release pushdown, par
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH 00/16] aio_context_acquire/release pushdown, part 2 |
Date: |
Thu, 19 Jan 2017 17:01:28 +0000 |
User-agent: |
Mutt/1.7.1 (2016-10-04) |
On Wed, Jan 18, 2017 at 05:31:03PM +0100, Paolo Bonzini wrote:
>
>
> On 18/01/2017 17:03, Stefan Hajnoczi wrote:
> > On Fri, Jan 13, 2017 at 02:17:15PM +0100, Paolo Bonzini wrote:
> >> This series pushes down aio_context_acquire/release to the point
> >> where we can actually reason on using different fine-grained mutexes.
> >>
> >> The main infrastructure is introduced in patch 1. The new API aio_co_wake
> >> starts a coroutine with aio_context_acquire/release protection, which
> >> requires tracking each coroutine's "home" AioContext. aio_co_schedule
> >> instead takes care of moving a sleeping coroutine to a different
> >> AioContext, also ensuring that it runs under aio_context_acquire/release.
> >> This is useful to implement bdrv_set_aio_context, as a simpler alternative
> >> to bottom halves. Even though one-shot BHs are already simpler than
> >> what we had before, after this patch aio_co_wake and aio_co_schedule
> >> save you from having to do aio_context_acquire/release explicitly.
> >>
> >> After patch 2 and 3, which are just small preparatory changes, patches
> >> 4 to 7 provide an example of how to use the new API. In particular patch
> >> 4 to 6 implement a new organization of coroutines in the NBD client,
> >> which allows not blocking on partial reply header reads.
> >>
> >> Patch 8 introduces helpers for AioContext locking in QED, which is
> >> the most complex AIO-based driver left. Then the actual meat of the
> >> series runs from patch 9 to patch 13, followed by small optimizations
> >> in patches 14 and 15.
> >>
> >> The patches do some back and forth in adding/removing
> >> aio_context_acquire/release calls in block/*.c but ultimately a small
> >> number of aio_context_acquire/release pairs are added after the pushdown.
> >> These are mostly in drivers that use external libraries (where they
> >> actually could already be replaced by QemuMutex) and in device models.
> >>
> >> Notably, coroutines need not care about aio_context_acquire/release.
> >> The device models ensure that the first creation of the coroutine has
> >> the AioContext, while aio_co_wake/aio_co_schedule do the same after
> >> they yield. Therefore, most of the files only need to use those two
> >> functions instead of, respectively, qemu_coroutine_enter and
> >> aio_bh_schedule_oneshot.
> >>
> >> However, this is only an intermediate step which is needed because the
> >> block layer and qemu-coroutine locks are thread-unsafe. So the next
> >> part will add separate locking, independent of AioContext, to block.c and
> >> mostly block/io.c---this includes making CoMutex thread-safe. Patch 16
> >> therefore already documents the current locking policies block.h to
> >> prepare for the next series.
> >>
> >> Paolo
> >>
> >> Paolo Bonzini (16):
> >> aio: introduce aio_co_schedule and aio_co_wake
> >> block-backend: allow blk_prw from coroutine context
> >> test-thread-pool: use generic AioContext infrastructure
> >> io: add methods to set I/O handlers on AioContext
> >> io: make qio_channel_yield aware of AioContexts
> >> nbd: do not block on partial reply header reads
> >> coroutine-lock: reschedule coroutine on the AioContext it was running
> >> on
> >> qed: introduce qed_aio_start_io and qed_aio_next_io_cb
> >> aio: push aio_context_acquire/release down to dispatching
> >> block: explicitly acquire aiocontext in timers that need it
> >> block: explicitly acquire aiocontext in callbacks that need it
> >> block: explicitly acquire aiocontext in bottom halves that need it
> >> block: explicitly acquire aiocontext in aio callbacks that need it
> >> aio-posix: partially inline aio_dispatch into aio_poll
> >> async: remove unnecessary inc/dec pairs
> >> block: document fields protected by AioContext lock
> >>
> >> aio-posix.c | 60 +++---------
> >> aio-win32.c | 30 ++----
> >> async.c | 81 ++++++++++++++--
> >> block/blkdebug.c | 9 +-
> >> block/blkreplay.c | 2 +-
> >> block/block-backend.c | 13 ++-
> >> block/curl.c | 44 ++++++---
> >> block/gluster.c | 9 +-
> >> block/io.c | 4 +-
> >> block/iscsi.c | 15 ++-
> >> block/linux-aio.c | 10 +-
> >> block/mirror.c | 12 ++-
> >> block/nbd-client.c | 108 ++++++++-------------
> >> block/nbd-client.h | 2 +-
> >> block/nfs.c | 9 +-
> >> block/qed-cluster.c | 2 +
> >> block/qed-table.c | 12 ++-
> >> block/qed.c | 58 +++++++----
> >> block/qed.h | 3 +
> >> block/sheepdog.c | 29 +++---
> >> block/ssh.c | 29 ++----
> >> block/throttle-groups.c | 2 +
> >> block/win32-aio.c | 9 +-
> >> dma-helpers.c | 2 +
> >> hw/block/virtio-blk.c | 19 +++-
> >> hw/scsi/scsi-bus.c | 2 +
> >> hw/scsi/scsi-disk.c | 15 +++
> >> hw/scsi/scsi-generic.c | 20 +++-
> >> hw/scsi/virtio-scsi.c | 6 ++
> >> include/block/aio.h | 38 +++++++-
> >> include/block/block_int.h | 64 ++++++++-----
> >> include/io/channel.h | 59 +++++++++++-
> >> include/qemu/coroutine_int.h | 10 +-
> >> include/sysemu/block-backend.h | 14 ++-
> >> io/channel-command.c | 13 +++
> >> io/channel-file.c | 11 +++
> >> io/channel-socket.c | 16 +++-
> >> io/channel-tls.c | 12 +++
> >> io/channel-watch.c | 6 ++
> >> io/channel.c | 97 +++++++++++++++----
> >> nbd/client.c | 2 +-
> >> nbd/common.c | 9 +-
> >> nbd/server.c | 4 +
> >> tests/Makefile.include | 15 ++-
> >> tests/iothread.c | 91 ++++++++++++++++++
> >> tests/iothread.h | 25 +++++
> >> tests/test-aio-multithread.c | 213
> >> +++++++++++++++++++++++++++++++++++++++++
> >> tests/test-thread-pool.c | 12 +--
> >> tests/test-vmstate.c | 11 ---
> >> thread-pool.c | 6 +-
> >> trace-events | 4 +
> >> util/qemu-coroutine-lock.c | 5 +-
> >> util/qemu-coroutine-sleep.c | 2 +-
> >> util/qemu-coroutine.c | 8 ++
> >> util/trace-events | 1 -
> >> 55 files changed, 1012 insertions(+), 352 deletions(-)
> >> create mode 100644 tests/iothread.c
> >> create mode 100644 tests/iothread.h
> >> create mode 100644 tests/test-aio-multithread.c
> >
> > This is a big and somewhat risky change. Have you run any performance
> > benchmarks?
>
> Not recently; I ran them a year ago and there was no measurable difference.
Good, please re-run for the final version.
signature.asc
Description: PGP signature
- Re: [Qemu-devel] [PATCH 11/16] block: explicitly acquire aiocontext in callbacks that need it, (continued)
- [Qemu-devel] [PATCH 14/16] aio-posix: partially inline aio_dispatch into aio_poll, Paolo Bonzini, 2017/01/13
- Re: [Qemu-devel] [PATCH 00/16] aio_context_acquire/release pushdown, part 2, Fam Zheng, 2017/01/16
- Re: [Qemu-devel] [PATCH 00/16] aio_context_acquire/release pushdown, part 2, Stefan Hajnoczi, 2017/01/18
- Re: [Qemu-devel] [PATCH 00/16] aio_context_acquire/release pushdown, part 2, Stefan Hajnoczi, 2017/01/18