From: Paolo Bonzini <pbonzini@redhat.com>
To: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>,
Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
"open list:Block layer core" <qemu-block@nongnu.org>,
qemu-devel <qemu-devel@nongnu.org>, Max Reitz <mreitz@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>,
John Snow <jsnow@redhat.com>
Subject: Re: [PATCH 5/6] co-shared-resource: protect with a mutex
Date: Fri, 14 May 2021 19:55:25 +0200 [thread overview]
Message-ID: <CABgObfamNZ_2XNHKgEBKXs0XjvhBXnqMVq6jYj+WDojBkJ9cDw@mail.gmail.com> (raw)
In-Reply-To: <6d1e432e-f18a-39a4-0bb6-2a14347c2905@redhat.com>
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Il ven 14 mag 2021, 16:10 Emanuele Giuseppe Esposito <eesposit@redhat.com>
ha scritto:
> > I'm not sure I like it since callers may still need coarser grained
> > locks to protect their own state or synchronize access to multiple
> > items of data. Also, some callers may not need thread-safety.
> >
> > Can the caller to be responsible for locking instead (e.g. using
> > CoMutex)?
>
> Right now co-shared-resource is being used only by block-copy, so I
> guess locking it from the caller or within the API won't really matter
> in this case.
>
> One possible idea on how to delegate this to the caller without adding
> additional small lock/unlock in block-copy is to move co_get_from_shres
> in block_copy_task_end, and calling it only when a boolean passed to
> block_copy_task_end is true.
>
The patch below won't work because qemu_co_queue_wait would have to unlock
the CoMutex; therefore you would have to pass it as an additional argument
to co_get_from_shres.
Overall, neither co_get_from_shres not AioTaskPool should be fast paths, so
using a local lock seems to produce the simplest API.
Paolo
> Otherwise make b_c_task_end always call co_get_from_shres and then
> include co_get_from_shres in block_copy_task_create, so that we always
> add and in case remove (if error) in the shared resource.
>
> Something like:
>
> diff --git a/block/block-copy.c b/block/block-copy.c
> index 3a447a7c3d..1e4914b0cb 100644
> --- a/block/block-copy.c
> +++ b/block/block-copy.c
> @@ -233,6 +233,7 @@ static coroutine_fn BlockCopyTask
> *block_copy_task_create(BlockCopyState *s,
> /* region is dirty, so no existent tasks possible in it */
> assert(!find_conflicting_task(s, offset, bytes));
> QLIST_INSERT_HEAD(&s->tasks, task, list);
> + co_get_from_shres(s->mem, task->bytes);
> qemu_co_mutex_unlock(&s->tasks_lock);
>
> return task;
> @@ -269,6 +270,7 @@ static void coroutine_fn
> block_copy_task_end(BlockCopyTask *task, int ret)
> bdrv_set_dirty_bitmap(task->s->copy_bitmap, task->offset,
> task->bytes);
> }
> qemu_co_mutex_lock(&task->s->tasks_lock);
> + co_put_to_shres(task->s->mem, task->bytes);
> task->s->in_flight_bytes -= task->bytes;
> QLIST_REMOVE(task, list);
> progress_set_remaining(task->s->progress,
> @@ -379,7 +381,6 @@ static coroutine_fn int
> block_copy_task_run(AioTaskPool *pool,
>
> aio_task_pool_wait_slot(pool);
> if (aio_task_pool_status(pool) < 0) {
> - co_put_to_shres(task->s->mem, task->bytes);
> block_copy_task_end(task, -ECANCELED);
> g_free(task);
> return -ECANCELED;
> @@ -498,7 +499,6 @@ static coroutine_fn int
> block_copy_task_entry(AioTask *task)
> }
> qemu_mutex_unlock(&t->s->calls_lock);
>
> - co_put_to_shres(t->s->mem, t->bytes);
> block_copy_task_end(t, ret);
>
> return ret;
> @@ -687,8 +687,6 @@ block_copy_dirty_clusters(BlockCopyCallState
> *call_state)
>
> trace_block_copy_process(s, task->offset);
>
> - co_get_from_shres(s->mem, task->bytes);
> -
> offset = task_end(task);
> bytes = end - offset;
>
>
>
>
> >
> >> diff --git a/util/qemu-co-shared-resource.c
> b/util/qemu-co-shared-resource.c
> >> index 1c83cd9d29..c455d02a1e 100644
> >> --- a/util/qemu-co-shared-resource.c
> >> +++ b/util/qemu-co-shared-resource.c
> >> @@ -32,6 +32,7 @@ struct SharedResource {
> >> uint64_t available;
> >>
> >> CoQueue queue;
> >> + QemuMutex lock;
> >
> > Please add a comment indicating what this lock protects.
> >
> > Thread safety should also be documented in the header file so API users
> > know what to expect.
>
> Will do, thanks.
>
> Emanuele
>
>
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next prev parent reply other threads:[~2021-05-14 17:56 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-10 8:59 [PATCH 0/6] block-copy: make helper APIs thread safe Emanuele Giuseppe Esposito
2021-05-10 8:59 ` [PATCH 1/6] ratelimit: treat zero speed as unlimited Emanuele Giuseppe Esposito
2021-05-10 11:00 ` Vladimir Sementsov-Ogievskiy
2021-05-10 8:59 ` [PATCH 2/6] block-copy: let ratelimit handle a speed of 0 Emanuele Giuseppe Esposito
2021-05-10 11:06 ` Vladimir Sementsov-Ogievskiy
2021-05-10 8:59 ` [PATCH 3/6] blockjob: " Emanuele Giuseppe Esposito
2021-05-10 11:17 ` Vladimir Sementsov-Ogievskiy
2021-05-10 8:59 ` [PATCH 4/6] progressmeter: protect with a mutex Emanuele Giuseppe Esposito
2021-05-10 11:28 ` Vladimir Sementsov-Ogievskiy
2021-05-10 16:52 ` Emanuele Giuseppe Esposito
2021-05-10 17:17 ` Vladimir Sementsov-Ogievskiy
2021-05-10 17:57 ` Emanuele Giuseppe Esposito
2021-05-11 12:28 ` Paolo Bonzini
2021-05-12 7:09 ` Vladimir Sementsov-Ogievskiy
2021-05-12 15:53 ` Stefan Hajnoczi
2021-05-10 8:59 ` [PATCH 5/6] co-shared-resource: " Emanuele Giuseppe Esposito
2021-05-10 11:40 ` Vladimir Sementsov-Ogievskiy
2021-05-11 8:34 ` Paolo Bonzini
2021-05-12 15:44 ` Stefan Hajnoczi
2021-05-12 18:30 ` Paolo Bonzini
2021-05-14 14:10 ` Emanuele Giuseppe Esposito
2021-05-14 14:26 ` Vladimir Sementsov-Ogievskiy via
2021-05-14 14:32 ` Emanuele Giuseppe Esposito
2021-05-14 15:30 ` Vladimir Sementsov-Ogievskiy via
2021-05-14 17:28 ` Emanuele Giuseppe Esposito
2021-05-14 21:15 ` Vladimir Sementsov-Ogievskiy via
2021-05-14 21:53 ` Emanuele Giuseppe Esposito
2021-05-15 7:11 ` Vladimir Sementsov-Ogievskiy via
2021-05-14 17:55 ` Paolo Bonzini [this message]
2021-05-10 8:59 ` [PATCH 6/6] aiopool: " Emanuele Giuseppe Esposito
2021-05-10 11:56 ` Vladimir Sementsov-Ogievskiy
2021-05-11 8:34 ` Paolo Bonzini
2021-05-12 15:19 ` Stefan Hajnoczi
2021-05-10 10:55 ` [PATCH 0/6] block-copy: make helper APIs thread safe Vladimir Sementsov-Ogievskiy
2021-05-12 14:24 ` Stefan Hajnoczi
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