Re: [PATCH v2 07/20] block/block-copy: add ratelimit to block-copy

[Max Reitz]

On 01.06.20 20:11, Vladimir Sementsov-Ogievskiy wrote:
> We are going to directly use one async block-copy operation for backup
> job, so we need rate limitator.

%s/limitator/limiter/g, I think.

> We want to maintain current backup behavior: only background copying is
> limited and copy-before-write operations only participate in limit
> calculation. Therefore we need one rate limitator for block-copy state
> and boolean flag for block-copy call state for actual limitation.
> 
> Note, that we can't just calculate each chunk in limitator after
> successful copying: it will not save us from starting a lot of async
> sub-requests which will exceed limit too much. Instead let's use the
> following scheme on sub-request creation:
> 1. If at the moment limit is not exceeded, create the request and
> account it immediately.
> 2. If at the moment limit is already exceeded, drop create sub-request
> and handle limit instead (by sleep).
> With this approach we'll never exceed the limit more than by one
> sub-request (which pretty much matches current backup behavior).

Sounds reasonable.

> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  include/block/block-copy.h |  8 +++++++
>  block/block-copy.c         | 44 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 52 insertions(+)
> 
> diff --git a/include/block/block-copy.h b/include/block/block-copy.h
> index 600984c733..d40e691123 100644
> --- a/include/block/block-copy.h
> +++ b/include/block/block-copy.h
> @@ -59,6 +59,14 @@ BlockCopyCallState *block_copy_async(BlockCopyState *s,
>                                       int64_t max_chunk,
>                                       BlockCopyAsyncCallbackFunc cb);
>  
> +/*
> + * Set speed limit for block-copy instance. All block-copy operations 
> related to
> + * this BlockCopyState will participate in speed calculation, but only
> + * block_copy_async calls with @ratelimit=true will be actually limited.
> + */
> +void block_copy_set_speed(BlockCopyState *s, BlockCopyCallState *call_state,
> +                          uint64_t speed);
> +
>  BdrvDirtyBitmap *block_copy_dirty_bitmap(BlockCopyState *s);
>  void block_copy_set_skip_unallocated(BlockCopyState *s, bool skip);
>  
> diff --git a/block/block-copy.c b/block/block-copy.c
> index 4114d1fd25..851d9c8aaf 100644
> --- a/block/block-copy.c
> +++ b/block/block-copy.c
> @@ -26,6 +26,7 @@
>  #define BLOCK_COPY_MAX_BUFFER (1 * MiB)
>  #define BLOCK_COPY_MAX_MEM (128 * MiB)
>  #define BLOCK_COPY_MAX_WORKERS 64
> +#define BLOCK_COPY_SLICE_TIME 100000000ULL /* ns */
>  
>  static coroutine_fn int block_copy_task_entry(AioTask *task);
>  
> @@ -36,11 +37,13 @@ typedef struct BlockCopyCallState {
>      int64_t bytes;
>      int max_workers;
>      int64_t max_chunk;
> +    bool ratelimit;
>      BlockCopyAsyncCallbackFunc cb;
>  
>      /* State */
>      bool failed;
>      bool finished;
> +    QemuCoSleepState *sleep_state;
>  
>      /* OUT parameters */
>      bool error_is_read;
> @@ -103,6 +106,9 @@ typedef struct BlockCopyState {
>      void *progress_opaque;
>  
>      SharedResource *mem;
> +
> +    uint64_t speed;
> +    RateLimit rate_limit;
>  } BlockCopyState;
>  
>  static BlockCopyTask *find_conflicting_task(BlockCopyState *s,
> @@ -611,6 +617,21 @@ block_copy_dirty_clusters(BlockCopyCallState *call_state)
>          }
>          task->zeroes = ret & BDRV_BLOCK_ZERO;
>  
> +        if (s->speed) {
> +            if (call_state->ratelimit) {
> +                uint64_t ns = ratelimit_calculate_delay(&s->rate_limit, 0);
> +                if (ns > 0) {
> +                    block_copy_task_end(task, -EAGAIN);
> +                    g_free(task);
> +                    qemu_co_sleep_ns_wakeable(QEMU_CLOCK_REALTIME, ns,
> +                                              &call_state->sleep_state);
> +                    continue;
> +                }
> +            }
> +
> +            ratelimit_calculate_delay(&s->rate_limit, task->bytes);
> +        }
> +

Looks good.

>          trace_block_copy_process(s, task->offset);
>  
>          co_get_from_shres(s->mem, task->bytes);
> @@ -649,6 +670,13 @@ out:
>      return ret < 0 ? ret : found_dirty;
>  }
>  
> +static void block_copy_kick(BlockCopyCallState *call_state)
> +{
> +    if (call_state->sleep_state) {
> +        qemu_co_sleep_wake(call_state->sleep_state);
> +    }
> +}
> +
>  /*
>   * block_copy_common
>   *
> @@ -729,6 +757,7 @@ BlockCopyCallState *block_copy_async(BlockCopyState *s,
>          .s = s,
>          .offset = offset,
>          .bytes = bytes,
> +        .ratelimit = ratelimit,

Hm, same problem/question as in patch 6: Should the @ratelimit parameter
really be added in patch 5 if it’s used only now?

>          .cb = cb,
>          .max_workers = max_workers ?: BLOCK_COPY_MAX_WORKERS,
>          .max_chunk = max_chunk,
> @@ -752,3 +781,18 @@ void block_copy_set_skip_unallocated(BlockCopyState *s, 
> bool skip)
>  {
>      s->skip_unallocated = skip;
>  }
> +
> +void block_copy_set_speed(BlockCopyState *s, BlockCopyCallState *call_state,
> +                          uint64_t speed)
> +{
> +    uint64_t old_speed = s->speed;
> +
> +    s->speed = speed;
> +    if (speed > 0) {
> +        ratelimit_set_speed(&s->rate_limit, speed, BLOCK_COPY_SLICE_TIME);
> +    }
> +
> +    if (call_state && old_speed && (speed > old_speed || speed == 0)) {
> +        block_copy_kick(call_state);
> +    }
> +}

Hm.  I’m interested in seeing how this is going to be used, i.e. what
callers will pass for @call_state.  I suppose it’s going to be the
background operation for the whole device, but I wonder whether it
actually makes sense to pass it.  I mean, the caller could just call
block_copy_kick() itself (unconditionally, because it’ll never hurt, I
think).

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