On Fri, Dec 5, 2014 at 9:58 PM, Martin K. Petersen
<martin.petersen@xxxxxxxxxx> wrote:
>>>>>> "Ming" == Ming Lei <ming.lei@xxxxxxxxxxxxx> writes:
>
>>> What about in READ CAPACITY(16)?
>
> Ming> It isn't set too.
>
> Please try the following patch:
>
>
> [SCSI] sd: Tweak discard heuristics to work around QEMU SCSI issue
>
> 7985090aa020 changed the discard heuristics to give preference to the
> WRITE SAME commands that (unlike UNMAP) guarantee deterministic results.
>
> Ming Lei discovered that QEMU SCSI's WRITE SAME implementation
> internally relied on limits that were only communicated for the UNMAP
I just found it should be one QEMU bug for emulating write same, but
limiting write same sectors number as max_unmap_blocks can
workaround the issue.
> case. And therefore discard commands backed by WRITE SAME would fail.
>
> Tweak the heuristics so we still pick UNMAP in the LBPRZ=0 case and only
> prefer the WRITE SAME variants if the device has the LBPRZ flag set.
>
> Reported-by: Ming Lei <ming.lei@xxxxxxxxxxxxx>
> Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
>
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index 95bfb7bfbb9d..76c5d1388417 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -2623,8 +2623,9 @@ static void sd_read_block_limits(struct scsi_disk *sdkp)
> sd_config_discard(sdkp, SD_LBP_WS16);
>
> } else { /* LBP VPD page tells us what to use */
> -
> - if (sdkp->lbpws)
> + if (sdkp->lbpu && sdkp->max_unmap_blocks && !sdkp->lbprz)
> + sd_config_discard(sdkp, SD_LBP_UNMAP);
> + else if (sdkp->lbpws)
> sd_config_discard(sdkp, SD_LBP_WS16);
> else if (sdkp->lbpws10)
> sd_config_discard(sdkp, SD_LBP_WS10);
Looks it does work.
Thanks,
Ming Lei
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