diff mbox series

ratelimit: protect with a mutex

Message ID 20210413125533.217440-1-pbonzini@redhat.com (mailing list archive)
State New
Headers show
Series ratelimit: protect with a mutex | expand

Commit Message

Paolo Bonzini April 13, 2021, 12:55 p.m. UTC
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(+)

Comments

Stefan Hajnoczi April 14, 2021, 10:46 a.m. UTC | #1
On Tue, Apr 13, 2021 at 02:55:33PM +0200, 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(+)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Emanuele Giuseppe Esposito April 14, 2021, 11:22 a.m. UTC | #2
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>
diff mbox series

Patch

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);
 }