On Fri, Sep 05, 2014 at 08:41:18PM +0200, Imre Palik wrote:
> From: "Palik, Imre" <im...@amazon.de>
>
> If the drbd backing device is a new device mapper device (e.g., a
> dm-linear mapping of an existing block device that contains data), the
> counters are initially 0 even though the device contains useful
> data. This causes throttling until something accesses the drbd device
> or the backing device.
What was wrong with my previous proposal?
How does changing the signedness help with
rs_last_events not being properly initialized?
Are you sure you have also considered all wrap-around cases?
Maybe you are too focused on your particular corner case
(disk_stats starting with 0).
Maybe I'm just thick right now, so please explain.
Lars
> The patch disables throttling, as long as only resync is responsible
> for disk activity on a freshly created device.
>
> Reported-by: Mikhail Sugakov <msuga...@amazon.de>
> Cc: Matt Wilson <m...@amazon.com>
> Signed-off-by: Imre Palik <im...@amazon.de>
> ---
> drivers/block/drbd/drbd_int.h | 4 ++--
> drivers/block/drbd/drbd_receiver.c | 10 +++++-----
> 2 files changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
> index 1a00001..298b1dc 100644
> --- a/drivers/block/drbd/drbd_int.h
> +++ b/drivers/block/drbd/drbd_int.h
> @@ -960,8 +960,8 @@ struct drbd_device {
> atomic_t rs_sect_in; /* for incoming resync data rate, SyncTarget */
> atomic_t rs_sect_ev; /* for submitted resync data rate, both */
> int rs_last_sect_ev; /* counter to compare with */
> - int rs_last_events; /* counter of read or write "events" (unit sectors)
> - * on the lower level device when we last looked.
> */
> + unsigned int rs_last_events; /* counter of read or write "events"
> (unit sectors)
> + * on the lower level device when we last
> looked. */
> int c_sync_rate; /* current resync rate after syncer throttle magic */
> struct fifo_buffer *rs_plan_s; /* correction values of resync planer
> (RCU, connection->conn_update) */
> int rs_in_flight; /* resync sectors in flight (to proxy, in proxy and
> from proxy) */
> diff --git a/drivers/block/drbd/drbd_receiver.c
> b/drivers/block/drbd/drbd_receiver.c
> index 9342b8d..147c917 100644
> --- a/drivers/block/drbd/drbd_receiver.c
> +++ b/drivers/block/drbd/drbd_receiver.c
> @@ -2467,7 +2467,7 @@ bool drbd_rs_c_min_rate_throttle(struct drbd_device
> *device)
> struct gendisk *disk = device->ldev->backing_bdev->bd_contains->bd_disk;
> unsigned long db, dt, dbdt;
> unsigned int c_min_rate;
> - int curr_events;
> + unsigned int curr_events;
>
> rcu_read_lock();
> c_min_rate = rcu_dereference(device->ldev->disk_conf)->c_min_rate;
> @@ -2477,12 +2477,12 @@ bool drbd_rs_c_min_rate_throttle(struct drbd_device
> *device)
> if (c_min_rate == 0)
> return false;
>
> - curr_events = (int)part_stat_read(&disk->part0, sectors[0]) +
> - (int)part_stat_read(&disk->part0, sectors[1]) -
> - atomic_read(&device->rs_sect_ev);
> + curr_events = (unsigned int)part_stat_read(&disk->part0, sectors[0]) +
> + (unsigned int)part_stat_read(&disk->part0, sectors[1]) -
> + (unsigned int)atomic_read(&device->rs_sect_ev);
>
> if (atomic_read(&device->ap_actlog_cnt)
> - || !device->rs_last_events || curr_events - device->rs_last_events
> > 64) {
> + || curr_events - device->rs_last_events > 64) {
> unsigned long rs_left;
> int i;
>
> --
> 1.7.9.5
>
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