Re: [Qemu-devel] [PATCH v12 3/5] block: add I/O throttling algorithm

[Kevin Wolf]

Am 03.11.2011 09:57, schrieb Zhi Yong Wu:
> Signed-off-by: Zhi Yong Wu <address@hidden>
> Signed-off-by: Stefan Hajnoczi <address@hidden>
> ---
>  block.c     |  220 
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  block.h     |    1 +
>  block_int.h |    1 +
>  3 files changed, 222 insertions(+), 0 deletions(-)
> 
> diff --git a/block.c b/block.c
> index 79e7f09..b2af48f 100644
> --- a/block.c
> +++ b/block.c
> @@ -74,6 +74,13 @@ static BlockDriverAIOCB 
> *bdrv_co_aio_rw_vector(BlockDriverState *bs,
>                                                 bool is_write);
>  static void coroutine_fn bdrv_co_do_rw(void *opaque);
>  
> +static bool bdrv_exceed_bps_limits(BlockDriverState *bs, int nb_sectors,
> +        bool is_write, double elapsed_time, uint64_t *wait);
> +static bool bdrv_exceed_iops_limits(BlockDriverState *bs, bool is_write,
> +        double elapsed_time, uint64_t *wait);
> +static bool bdrv_exceed_io_limits(BlockDriverState *bs, int nb_sectors,
> +        bool is_write, int64_t *wait);
> +
>  static QTAILQ_HEAD(, BlockDriverState) bdrv_states =
>      QTAILQ_HEAD_INITIALIZER(bdrv_states);
>  
> @@ -107,6 +114,24 @@ int is_windows_drive(const char *filename)
>  #endif
>  
>  /* throttling disk I/O limits */
> +void bdrv_io_limits_disable(BlockDriverState *bs)
> +{
> +    bs->io_limits_enabled = false;
> +
> +    while (qemu_co_queue_next(&bs->throttled_reqs));
> +
> +    if (bs->block_timer) {
> +        qemu_del_timer(bs->block_timer);
> +        qemu_free_timer(bs->block_timer);
> +        bs->block_timer = NULL;
> +    }
> +
> +    bs->slice_start = 0;
> +    bs->slice_end   = 0;
> +    bs->slice_time  = 0;
> +    memset(&bs->io_base, 0, sizeof(bs->io_base));
> +}
> +
>  static void bdrv_block_timer(void *opaque)
>  {
>      BlockDriverState *bs = opaque;
> @@ -136,6 +161,31 @@ bool bdrv_io_limits_enabled(BlockDriverState *bs)
>           || io_limits->iops[BLOCK_IO_LIMIT_TOTAL];
>  }
>  
> +static void bdrv_io_limits_intercept(BlockDriverState *bs,
> +                                     bool is_write, int nb_sectors)
> +{
> +    int64_t wait_time = -1;
> +
> +    if (!qemu_co_queue_empty(&bs->throttled_reqs)) {
> +        qemu_co_queue_wait(&bs->throttled_reqs);
> +    }
> +
> +    /* In fact, we hope to keep each request's timing, in FIFO mode. The next
> +     * throttled requests will not be dequeued until the current request is
> +     * allowed to be serviced. So if the current request still exceeds the
> +     * limits, it will be inserted to the head. All requests followed it will
> +     * be still in throttled_reqs queue.
> +     */
> +
> +    while (bdrv_exceed_io_limits(bs, nb_sectors, is_write, &wait_time)) {
> +        qemu_mod_timer(bs->block_timer,
> +                       wait_time + qemu_get_clock_ns(vm_clock));
> +        qemu_co_queue_wait_insert_head(&bs->throttled_reqs);
> +    }
> +
> +    qemu_co_queue_next(&bs->throttled_reqs);
> +}
> +
>  /* check if the path starts with "<protocol>:" */
>  static int path_has_protocol(const char *path)
>  {
> @@ -718,6 +768,11 @@ int bdrv_open(BlockDriverState *bs, const char 
> *filename, int flags,
>          bdrv_dev_change_media_cb(bs, true);
>      }
>  
> +    /* throttling disk I/O limits */
> +    if (bs->io_limits_enabled) {
> +        bdrv_io_limits_enable(bs);
> +    }
> +
>      return 0;
>  
>  unlink_and_fail:
> @@ -753,6 +808,11 @@ void bdrv_close(BlockDriverState *bs)
>  
>          bdrv_dev_change_media_cb(bs, false);
>      }
> +
> +    /*throttling disk I/O limits*/
> +    if (bs->io_limits_enabled) {
> +        bdrv_io_limits_disable(bs);
> +    }
>  }
>  
>  void bdrv_close_all(void)
> @@ -1291,6 +1351,11 @@ static int coroutine_fn 
> bdrv_co_do_readv(BlockDriverState *bs,
>          return -EIO;
>      }
>  
> +    /* throttling disk read I/O */
> +    if (bs->io_limits_enabled) {
> +        bdrv_io_limits_intercept(bs, false, nb_sectors);
> +    }
> +
>      return drv->bdrv_co_readv(bs, sector_num, nb_sectors, qiov);
>  }
>  
> @@ -1321,6 +1386,11 @@ static int coroutine_fn 
> bdrv_co_do_writev(BlockDriverState *bs,
>          return -EIO;
>      }
>  
> +    /* throttling disk write I/O */
> +    if (bs->io_limits_enabled) {
> +        bdrv_io_limits_intercept(bs, true, nb_sectors);
> +    }
> +
>      ret = drv->bdrv_co_writev(bs, sector_num, nb_sectors, qiov);
>  
>      if (bs->dirty_bitmap) {
> @@ -2512,6 +2582,156 @@ void bdrv_aio_cancel(BlockDriverAIOCB *acb)
>      acb->pool->cancel(acb);
>  }
>  
> +/* block I/O throttling */
> +static bool bdrv_exceed_bps_limits(BlockDriverState *bs, int nb_sectors,
> +                 bool is_write, double elapsed_time, uint64_t *wait) {
> +    uint64_t bps_limit = 0;
> +    double   bytes_limit, bytes_base, bytes_res;
> +    double   slice_time, wait_time;
> +
> +    if (bs->io_limits.bps[BLOCK_IO_LIMIT_TOTAL]) {
> +        bps_limit = bs->io_limits.bps[BLOCK_IO_LIMIT_TOTAL];
> +    } else if (bs->io_limits.bps[is_write]) {
> +        bps_limit = bs->io_limits.bps[is_write];
> +    } else {
> +        if (wait) {
> +            *wait = 0;
> +        }
> +
> +        return false;
> +    }
> +
> +    slice_time = bs->slice_end - bs->slice_start;
> +    slice_time /= (NANOSECONDS_PER_SECOND);
> +    bytes_limit = bps_limit * slice_time;
> +    bytes_base  = bs->nr_bytes[is_write] - bs->io_base.bytes[is_write];
> +    if (bs->io_limits.bps[BLOCK_IO_LIMIT_TOTAL]) {
> +        bytes_base += bs->nr_bytes[!is_write] - bs->io_base.bytes[!is_write];
> +    }
> +
> +    bytes_res   = (unsigned) nb_sectors * BDRV_SECTOR_SIZE;
> +
> +    if (bytes_base + bytes_res <= bytes_limit) {
> +        if (wait) {
> +            *wait = 0;
> +        }
> +
> +        return false;
> +    }
> +
> +    /* Calc approx time to dispatch */
> +    wait_time = (bytes_base + bytes_res) / bps_limit - elapsed_time;
> +
> +    bs->slice_time = wait_time * BLOCK_IO_SLICE_TIME * 10;
> +    bs->slice_end += bs->slice_time - 3 * BLOCK_IO_SLICE_TIME;
> +    if (wait) {
> +        *wait = wait_time * BLOCK_IO_SLICE_TIME * 10;
> +    }

I'm not quire sure what bs->slice_end really is and what these
calculations do exactly. Looks like magic. Can you add some comments
that explain why slice_end is increased and how you estimate *wait?

> +
> +    return true;
> +}
> +
> +static bool bdrv_exceed_iops_limits(BlockDriverState *bs, bool is_write,
> +                             double elapsed_time, uint64_t *wait) {

Coding style requires the brace on its own line.

> +    uint64_t iops_limit = 0;
> +    double   ios_limit, ios_base;
> +    double   slice_time, wait_time;
> +
> +    if (bs->io_limits.iops[BLOCK_IO_LIMIT_TOTAL]) {
> +        iops_limit = bs->io_limits.iops[BLOCK_IO_LIMIT_TOTAL];
> +    } else if (bs->io_limits.iops[is_write]) {
> +        iops_limit = bs->io_limits.iops[is_write];
> +    } else {
> +        if (wait) {
> +            *wait = 0;
> +        }
> +
> +        return false;
> +    }
> +
> +    slice_time = bs->slice_end - bs->slice_start;
> +    slice_time /= (NANOSECONDS_PER_SECOND);
> +    ios_limit  = iops_limit * slice_time;
> +    ios_base   = bs->nr_ops[is_write] - bs->io_base.ios[is_write];
> +    if (bs->io_limits.iops[BLOCK_IO_LIMIT_TOTAL]) {
> +        ios_base += bs->nr_ops[!is_write] - bs->io_base.ios[!is_write];
> +    }
> +
> +    if (ios_base + 1 <= ios_limit) {
> +        if (wait) {
> +            *wait = 0;
> +        }
> +
> +        return false;
> +    }
> +
> +    /* Calc approx time to dispatch */
> +    wait_time = (ios_base + 1) / iops_limit;
> +    if (wait_time > elapsed_time) {
> +        wait_time = wait_time - elapsed_time;
> +    } else {
> +        wait_time = 0;
> +    }
> +
> +    bs->slice_time = wait_time * BLOCK_IO_SLICE_TIME * 10;
> +    bs->slice_end += bs->slice_time - 3 * BLOCK_IO_SLICE_TIME;
> +    if (wait) {
> +        *wait = wait_time * BLOCK_IO_SLICE_TIME * 10;
> +    }
> +
> +    return true;
> +}
> +
> +static bool bdrv_exceed_io_limits(BlockDriverState *bs, int nb_sectors,
> +                           bool is_write, int64_t *wait) {

Same here.

Kevin