Re: [PATCH] scsi: libsas: Add SMP request allocation handler callback

[Jason Yan]

On 2024/3/25 22:03, Damien Le Moal wrote:
> On 3/25/24 22:17, Yihang Li wrote:
> > This series [1] reducing the kmalloc() minimum alignment on arm64 to 8
> > (from 128).
>
> And ? What is the point you are trying to convey here ?
>
> > The hisi_sas has special requirements on the memory address alignment
> > (must be 16-byte-aligned) of the command request frame, so add a SMP
> > request allocation callback and fill it in for the hisi_sas driver.
>
> 128 is aligned to 16. So what is the problem you are trying to solve here ?
> Can you clarify ? I suspect this is all about memory allocation optimization ?

After series [1] been merged, kmalloc is 8-byte-aligned, however 
hisi_sas hardware needs 16-byte-aligned. That's the problem.

> > Link: https://lkml.kernel.org/r/20230612153201.554742-1-catalin.marinas@xxxxxxx [1]
> > Signed-off-by: Yihang Li <liyihang9@xxxxxxxxxx>
> > ---
> >   drivers/scsi/hisi_sas/hisi_sas_main.c | 14 ++++++++++++
> >   drivers/scsi/libsas/sas_expander.c    | 31 ++++++++++++++++++---------
> >   include/scsi/libsas.h                 |  3 +++
> >   3 files changed, 38 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/scsi/hisi_sas/hisi_sas_main.c b/drivers/scsi/hisi_sas/hisi_sas_main.c
> > index 097dfe4b620d..40329558d435 100644
> > --- a/drivers/scsi/hisi_sas/hisi_sas_main.c
> > +++ b/drivers/scsi/hisi_sas/hisi_sas_main.c
> > @@ -2031,6 +2031,19 @@ static int hisi_sas_write_gpio(struct sas_ha_struct *sha, u8 reg_type,
> >   				reg_index, reg_count, write_data);
> >   }
> >   
> > +static void *hisi_sas_alloc_smp_req(int size)
> > +{
> > +	u8 *p;
> > +
> > +	/* The address must be 16-byte-aligned. */
>
> ARCH_DMA_MINALIGN is not always 16, right ?
>
> > +	size = ALIGN(size, ARCH_DMA_MINALIGN);
> > +	p = kzalloc(size, GFP_KERNEL);
> > +	if (p)
> > +		p[0] = SMP_REQUEST;
> > +
> > +	return p;
> > +}
> > +
> >   static void hisi_sas_phy_disconnected(struct hisi_sas_phy *phy)
> >   {
> >   	struct asd_sas_phy *sas_phy = &phy->sas_phy;
> > @@ -2130,6 +2143,7 @@ static struct sas_domain_function_template hisi_sas_transport_ops = {
> >   	.lldd_write_gpio	= hisi_sas_write_gpio,
> >   	.lldd_tmf_aborted	= hisi_sas_tmf_aborted,
> >   	.lldd_abort_timeout	= hisi_sas_internal_abort_timeout,
> > +	.lldd_alloc_smp_req	= hisi_sas_alloc_smp_req,
>
> Why this complexity ? Why not simply modify alloc_smp_req() to have the required
> alignment ? This will avoid a costly indirect function call.

Yeah, I think it's simpler to modify alloc_smp_req() directly too. 
Yihang, Can you please cook a new one?

Thansk,
Jason