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Message-ID: <bbf8376a-fcab-0aaf-e834-379a72672496@huawei.com>
Date: Tue, 26 Mar 2024 14:34:36 +0800
From: Yihang Li <liyihang9@...wei.com>
To: Jason Yan <yanaijie@...wei.com>, Damien Le Moal <dlemoal@...nel.org>,
<jejb@...ux.ibm.com>, <martin.petersen@...cle.com>,
<john.g.garry@...cle.com>, <chenxiang66@...ilicon.com>
CC: <linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<linuxarm@...wei.com>, <prime.zeng@...wei.com>, <yangxingui@...wei.com>,
<liyihang9@...wei.com>
Subject: Re: [PATCH] scsi: libsas: Add SMP request allocation handler callback
On 2024/3/25 22:21, Jason Yan wrote:
> 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.
Yes, that's the problem. I will explain it in detail in the next version.
>
>>
>>>
>>> Link: https://lkml.kernel.org/r/20230612153201.554742-1-catalin.marinas@arm.com [1]
>>> Signed-off-by: Yihang Li <liyihang9@...wei.com>
>>> ---
>>> 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?
Sure, I will post a new version later.
The reason why I did not directly modify alloc_smp_req() is that I think the requirement that the command frame must be 16-byte aligned is hisi_sas private and not a general requirement.
To avoid the impact on other drivers, I only add aligned to 16B in hisi_sas. If this measure is considered pointless, I will directly modify alloc_smp_req().
Thanks,
Yihang
>
> Thansk,
> Jason
> .
>
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