Re: [PATCH v3 10/13] bcache: fix inaccurate io state for detached bcache devices

[Hannes Reinecke <hare@suse.de>]

On 01/14/2018 03:42 PM, Coly Li wrote:
> From: Tang Junhui <tang.junhui@zte.com.cn>
> 
> When we run IO in a detached device,  and run iostat to shows IO status,
> normally it will show like bellow (Omitted some fields):
> Device: ... avgrq-sz avgqu-sz   await r_await w_await  svctm  %util
> sdd        ... 15.89     0.53    1.82    0.20    2.23   1.81  52.30
> bcache0    ... 15.89   115.42    0.00    0.00    0.00   2.40  69.60
> but after IO stopped, there are still very big avgqu-sz and %util
> values as bellow:
> Device: ... avgrq-sz avgqu-sz   await r_await w_await  svctm  %util
> bcache0   ...      0   5326.32    0.00    0.00    0.00   0.00 100.10
> 
> The reason for this issue is that, only generic_start_io_acct() called
> and no generic_end_io_acct() called for detached device in
> cached_dev_make_request(). See the code:
> //start generic_start_io_acct()
> generic_start_io_acct(q, rw, bio_sectors(bio), &d->disk->part0);
> if (cached_dev_get(dc)) {
> 	//will callback generic_end_io_acct()
> }
> else {
> 	//will not call generic_end_io_acct()
> }
> 
> This patch calls generic_end_io_acct() in the end of IO for detached
> devices, so we can show IO state correctly.
> 
> (Modified to use GFP_NOIO in kzalloc() by Coly Li)
> 
> Signed-off-by: Tang Junhui <tang.junhui@zte.com.cn>
> Reviewed-by: Coly Li <colyli@suse.de>
> ---
>  drivers/md/bcache/request.c | 58 +++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 51 insertions(+), 7 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.com>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
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