From: Emanuele Giuseppe Esposito <eesposit@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org
Cc: stefanha@redhat.com, qemu-block@nongnu.org
Subject: Re: [PATCH] ratelimit: protect with a mutex
Date: Wed, 14 Apr 2021 13:22:27 +0200 [thread overview]
Message-ID: <76ab1570-e8d2-889d-f8f9-7a00cb810880@redhat.com> (raw)
In-Reply-To: <20210413125533.217440-1-pbonzini@redhat.com>
On 13/04/2021 14:55, Paolo Bonzini wrote:
> Right now, rate limiting is protected by the AioContext mutex, which is
> taken for example both by the block jobs and by qmp_block_job_set_speed
> (via find_block_job).
>
> We would like to remove the dependency of block layer code on the
> AioContext mutex, since most drivers and the core I/O code are already
> not relying on it. However, there is no existing lock that can easily
> be taken by both ratelimit_set_speed and ratelimit_calculate_delay,
> especially because the latter might run in coroutine context (and
> therefore under a CoMutex) but the former will not.
>
> Since concurrent calls to ratelimit_calculate_delay are not possible,
> one idea could be to use a seqlock to get a snapshot of slice_ns and
> slice_quota. But for now keep it simple, and just add a mutex to the
> RateLimit struct; block jobs are generally not performance critical to
> the point of optimizing the clock cycles spent in synchronization.
>
> This also requires the introduction of init/destroy functions, so
> add them to the two users of ratelimit.h.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> block/block-copy.c | 2 ++
> blockjob.c | 3 +++
> include/qemu/ratelimit.h | 14 ++++++++++++++
> 3 files changed, 19 insertions(+)
>
> diff --git a/block/block-copy.c b/block/block-copy.c
> index 39ae481c8b..9b4af00614 100644
> --- a/block/block-copy.c
> +++ b/block/block-copy.c
> @@ -230,6 +230,7 @@ void block_copy_state_free(BlockCopyState *s)
> return;
> }
>
> + ratelimit_destroy(&s->rate_limit);
> bdrv_release_dirty_bitmap(s->copy_bitmap);
> shres_destroy(s->mem);
> g_free(s);
> @@ -289,6 +290,7 @@ BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
> s->copy_size = MAX(s->cluster_size, BLOCK_COPY_MAX_BUFFER);
> }
>
> + ratelimit_init(&s->rate_limit);
> QLIST_INIT(&s->tasks);
> QLIST_INIT(&s->calls);
>
> diff --git a/blockjob.c b/blockjob.c
> index 207e8c7fd9..46f15befe8 100644
> --- a/blockjob.c
> +++ b/blockjob.c
> @@ -87,6 +87,7 @@ void block_job_free(Job *job)
>
> block_job_remove_all_bdrv(bjob);
> blk_unref(bjob->blk);
> + ratelimit_destroy(&bjob->limit);
> error_free(bjob->blocker);
> }
>
> @@ -435,6 +436,8 @@ void *block_job_create(const char *job_id, const BlockJobDriver *driver,
> assert(job->job.driver->free == &block_job_free);
> assert(job->job.driver->user_resume == &block_job_user_resume);
>
> + ratelimit_init(&job->limit);
> +
> job->blk = blk;
>
> job->finalize_cancelled_notifier.notify = block_job_event_cancelled;
> diff --git a/include/qemu/ratelimit.h b/include/qemu/ratelimit.h
> index 01da8d63f1..003ea6d5a3 100644
> --- a/include/qemu/ratelimit.h
> +++ b/include/qemu/ratelimit.h
> @@ -14,9 +14,11 @@
> #ifndef QEMU_RATELIMIT_H
> #define QEMU_RATELIMIT_H
>
> +#include "qemu/lockable.h"
> #include "qemu/timer.h"
>
> typedef struct {
> + QemuMutex lock;
> int64_t slice_start_time;
> int64_t slice_end_time;
> uint64_t slice_quota;
> @@ -40,6 +42,7 @@ static inline int64_t ratelimit_calculate_delay(RateLimit *limit, uint64_t n)
> int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
> double delay_slices;
>
> + QEMU_LOCK_GUARD(&limit->lock);
> assert(limit->slice_quota && limit->slice_ns);
>
> if (limit->slice_end_time < now) {
> @@ -65,9 +68,20 @@ static inline int64_t ratelimit_calculate_delay(RateLimit *limit, uint64_t n)
> return limit->slice_end_time - now;
> }
>
> +static inline void ratelimit_init(RateLimit *limit)
> +{
> + qemu_mutex_init(&limit->lock);
> +}
> +
> +static inline void ratelimit_destroy(RateLimit *limit)
> +{
> + qemu_mutex_destroy(&limit->lock);
> +}
> +
> static inline void ratelimit_set_speed(RateLimit *limit, uint64_t speed,
> uint64_t slice_ns)
> {
> + QEMU_LOCK_GUARD(&limit->lock);
> limit->slice_ns = slice_ns;
> limit->slice_quota = MAX(((double)speed * slice_ns) / 1000000000ULL, 1);
> }
>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
next prev parent reply other threads:[~2021-04-14 11:24 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-13 12:55 [PATCH] ratelimit: protect with a mutex Paolo Bonzini
2021-04-14 10:46 ` Stefan Hajnoczi
2021-04-14 11:22 ` Emanuele Giuseppe Esposito [this message]
2021-05-10 9:51 ` Vladimir Sementsov-Ogievskiy
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=76ab1570-e8d2-889d-f8f9-7a00cb810880@redhat.com \
--to=eesposit@redhat.com \
--cc=pbonzini@redhat.com \
--cc=qemu-block@nongnu.org \
--cc=qemu-devel@nongnu.org \
--cc=stefanha@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).