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From:   Changheun Lee <nanich.lee@samsung.com>
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Subject: Re: [PATCH v7 2/3] ufs: set QUEUE_FLAG_LIMIT_BIO_SIZE
Date:   Wed, 14 Apr 2021 10:40:18 +0900
Message-Id: <20210414014018.20318-1-nanich.lee@samsung.com>
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> On 4/12/21 7:55 PM, Changheun Lee wrote:
> > Set QUEUE_FLAG_LIMIT_BIO_SIZE queue flag to limit bio max size to
> > queue max sectors size for UFS device.
> > 
> > Signed-off-by: Changheun Lee <nanich.lee@samsung.com>
> > ---
> >  drivers/scsi/scsi_lib.c   | 2 ++
> >  drivers/scsi/ufs/ufshcd.c | 1 +
> >  include/scsi/scsi_host.h  | 2 ++
> >  3 files changed, 5 insertions(+)
> > 
> > diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> > index 7d52a11e1b61..73ce6ba7903a 100644
> > --- a/drivers/scsi/scsi_lib.c
> > +++ b/drivers/scsi/scsi_lib.c
> > @@ -1838,6 +1838,8 @@ void __scsi_init_queue(struct Scsi_Host *shost, struct request_queue *q)
> >  	 * Devices that require a bigger alignment can increase it later.
> >  	 */
> >  	blk_queue_dma_alignment(q, max(4, dma_get_cache_alignment()) - 1);
> > +
> > +	blk_queue_set_limit_bio_size(q, shost->limit_bio_size);
> >  }
> >  EXPORT_SYMBOL_GPL(__scsi_init_queue);
> >  
> > diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> > index d3d05e997c13..000eb5ab022e 100644
> > --- a/drivers/scsi/ufs/ufshcd.c
> > +++ b/drivers/scsi/ufs/ufshcd.c
> > @@ -9313,6 +9313,7 @@ int ufshcd_init(struct ufs_hba *hba, void __iomem *mmio_base, unsigned int irq)
> >  	host->max_channel = UFSHCD_MAX_CHANNEL;
> >  	host->unique_id = host->host_no;
> >  	host->max_cmd_len = UFS_CDB_SIZE;
> > +	host->limit_bio_size = true;
> >  
> >  	hba->max_pwr_info.is_valid = false;
> >  
> > diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
> > index e30fd963b97d..486f61588717 100644
> > --- a/include/scsi/scsi_host.h
> > +++ b/include/scsi/scsi_host.h
> > @@ -607,6 +607,8 @@ struct Scsi_Host {
> >  	unsigned int max_segment_size;
> >  	unsigned long dma_boundary;
> >  	unsigned long virt_boundary_mask;
> > +	unsigned int limit_bio_size;
> > +
> >  	/*
> >  	 * In scsi-mq mode, the number of hardware queues supported by the LLD.
> >  	 *
> 
> This patch should have been split into one patch for the SCSI core and
> another patch for the UFS driver.
> 
> I see an issue with this patch: a new attribute has been introduced in
> struct Scsi_Host but it is not used by the SCSI core. That seems weird
> to me.
> 
> Another comment I have about this patch is why to restrict the BIO size
> (blk_queue_set_limit_bio_size(q, shost->limit_bio_size)) only for UFS
> devices? Aren't all block devices, including NVMe devices, expected to
> benefit from limiting the BIO size if no stacking is involved? How about
> the following approach?
> * In blk_queue_max_hw_sectors(), set the maximum BIO size to
> max_hw_sectors. As you may know blk_queue_max_hw_sectors() may be
> called by any block driver (stacking and non-stacking).
> * In blk_stack_limits(), set the maximum BIO size to UINT_MAX. Stacking
> block drivers must call blk_stack_limits().

I think it will be good for all block device too, but it might be not in
some environment. I got a feedback about it. So I specified to UFS only.
I see what you said. I'll try as your approach.

> 
> Thanks,
> 
> Bart.


Thanks,

Changheun Lee.