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SubjectRe: [PATCH] scsi: ufs: add a quirk to disable FUA support
On 06/01, Adrian Hunter wrote:
> On 31/05/22 23:10, Jaegeuk Kim wrote:
> > UFS stack shows very low performance of FUA comparing to write and cache_flush.
> > Let's add a quirk to adjust it.
> >
> > E.g., average latency according to the chunk size of write
> >
> > Write(us/KB) 4 64 256 1024 2048
> > FUA 873.792 754.604 995.624 1011.67 1067.99
> > CACHE_FLUSH 824.703 712.98 800.307 1019.5 1037.37
>
> Wouldn't it depend on how much data might be in the cache?

I've got this average latency from 100 commands of write+cache_flush vs.
write(FUA). I think the cached data should be the same as this chunk
size.

> Do you have real-world use-cases where the difference is measurable?

I'm approaching this based on 1) f2fs uses FUA for checkpoint and fsync,
and 2) iomap uses FUA for O_DIRECT|O_DSYNC case [1].

[1] https://lore.kernel.org/lkml/20220527205955.3251982-1-jaegeuk@kernel.org/

>
> >
> > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> > ---
> > drivers/scsi/ufs/ufshcd.c | 3 +++
> > drivers/scsi/ufs/ufshcd.h | 5 +++++
> > 2 files changed, 8 insertions(+)
> >
> > diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> > index 3f9caafa91bf..811f3467879c 100644
> > --- a/drivers/scsi/ufs/ufshcd.c
> > +++ b/drivers/scsi/ufs/ufshcd.c
> > @@ -5035,6 +5035,9 @@ static int ufshcd_slave_configure(struct scsi_device *sdev)
> > */
> > sdev->silence_suspend = 1;
> >
> > + if (hba->quirks & UFSHCD_QUIRK_BROKEN_FUA)
> > + sdev->broken_fua = 1;
> > +
> > ufshcd_crypto_register(hba, q);
> >
> > return 0;
> > diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
> > index 94f545be183a..6c480c6741d6 100644
> > --- a/drivers/scsi/ufs/ufshcd.h
> > +++ b/drivers/scsi/ufs/ufshcd.h
> > @@ -602,6 +602,11 @@ enum ufshcd_quirks {
> > * support physical host configuration.
> > */
> > UFSHCD_QUIRK_SKIP_PH_CONFIGURATION = 1 << 16,
> > +
> > + /*
> > + * This quirk disables FUA support.
> > + */
> > + UFSHCD_QUIRK_BROKEN_FUA = 1 << 17,
>
> Wouldn't it be more appropriate to make it a UFS_DEVICE_QUIRK_
> since it presumably depends on the UFS device not the host controller?
>
> Also, as already commented by others, there needs to be a user of
> the quirk

Since I asked SoC vendors can verify the performance with this quirk,
I need to wait for their reply. Meanwhile, I'm willing to disable FUA in Pixel
devices, which I cannot post any patch directly to LKML.

Agreed that, if there's no other user in upstream, I'm okay to drop
this.

>
> > };
> >
> > enum ufshcd_caps {

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