From: Can Guo <cang@codeaurora.org>
To: Bart Van Assche <bvanassche@acm.org>
Cc: asutoshd@codeaurora.org, nguyenb@codeaurora.org,
hongwus@codeaurora.org, linux-scsi@vger.kernel.org,
kernel-team@android.com, Stanley Chu <stanley.chu@mediatek.com>,
Alim Akhtar <alim.akhtar@samsung.com>,
Avri Altman <avri.altman@wdc.com>,
"James E.J. Bottomley" <jejb@linux.ibm.com>,
"Martin K. Petersen" <martin.petersen@oracle.com>,
Matthias Brugger <matthias.bgg@gmail.com>,
Bean Huo <beanhuo@micron.com>, Jaegeuk Kim <jaegeuk@kernel.org>,
Adrian Hunter <adrian.hunter@intel.com>,
Kiwoong Kim <kwmad.kim@samsung.com>,
Satya Tangirala <satyat@google.com>,
open list <linux-kernel@vger.kernel.org>,
"moderated list:ARM/Mediatek SoC support"
<linux-arm-kernel@lists.infradead.org>,
"moderated list:ARM/Mediatek SoC support"
<linux-mediatek@lists.infradead.org>
Subject: Re: [PATCH v1 2/3] scsi: ufs: Optimize host lock on transfer requests send/compl paths
Date: Tue, 25 May 2021 09:40:18 +0800 [thread overview]
Message-ID: <0cfbf580e340073ff972be493a59dbe7@codeaurora.org> (raw)
In-Reply-To: <41a08b3e-122d-4f1a-abbd-4b5730f880b2@acm.org>
On 2021-05-25 04:10, Bart Van Assche wrote:
> On 5/24/21 1:36 AM, Can Guo wrote:
>> Current UFS IRQ handler is completely wrapped by host lock, and
>> because
>> ufshcd_send_command() is also protected by host lock, when IRQ handler
>> fires, not only the CPU running the IRQ handler cannot send new
>> requests,
>> the rest CPUs can neither. Move the host lock wrapping the IRQ handler
>> into
>> specific branches, i.e., ufshcd_uic_cmd_compl(),
>> ufshcd_check_errors(),
>> ufshcd_tmc_handler() and ufshcd_transfer_req_compl(). Meanwhile, to
>> further
>> reduce occpuation of host lock in ufshcd_transfer_req_compl(), host
>> lock is
>> no longer required to call __ufshcd_transfer_req_compl(). As per test,
>> the
>> optimization can bring considerable gain to random read/write
>> performance.
>
> Hi Can,
>
> Using the host lock to serialize the completion path against the
> submission path was a common practice 11 years ago, before the host
> lock
> push-down (see also
> https://linux-scsi.vger.kernel.narkive.com/UEmGgwAc/rfc-patch-scsi-host-lock-push-down).
> Modern SCSI LLDs should not use the SCSI host lock. Please consider
> introducing one or more new synchronization objects in struct ufs_hba
> and to use these instead of the SCSI host lock. That will save multiple
> pointer dereferences in the hot path since hba->host->host_lock will
> become hba->new_spin_lock.
>
> An additional question is whether it is necessary for v3.0 UFS devices
> to serialize the submission path against the completion path? Multiple
> high-performance SCSI LLDs support hardware with separate submission
> and
> completion queues and hence do not need any serialization between the
> submission and the completion path. I'm asking this because it is
> likely
> that sooner or later multiqueue support will be added in the UFS
> specification. Benefiting from multiqueue support will require to
> rework
> locking in the UFS driver anyway.
>
Hi Bart,
Agree with all above, and what you ask is right what we are doing in the
3rd change - get rid of host lock on dispatch and completion paths.
I agree with using dedicated spin locks for dedicated purposes in UFS
driver,
e.g., clk gating has its own gating_lock and clk scaling has its own
scaling_lock.
But this specific series is only for improving performance. We will take
your
comments into consideration and address it in future.
Thanks,
Can Guo.
> Thanks,
>
> Bart.
next prev parent reply other threads:[~2021-05-25 1:40 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-24 8:36 [PATCH v1 0/3] Optimize host lock on TR send/compl paths and utilize UTRLCNR Can Guo
2021-05-24 8:36 ` [PATCH v1 1/3] scsi: ufs: Remove a redundant command completion logic in error handler Can Guo
2021-05-24 16:43 ` Bart Van Assche
2021-05-25 4:15 ` Stanley Chu
2021-05-31 7:14 ` Bean Huo
2021-05-24 8:36 ` [PATCH v1 2/3] scsi: ufs: Optimize host lock on transfer requests send/compl paths Can Guo
2021-05-24 11:25 ` kernel test robot
2021-06-08 17:53 ` Nathan Chancellor
2021-06-09 1:01 ` Can Guo
2021-05-24 20:10 ` Bart Van Assche
2021-05-25 1:34 ` Asutosh Das (asd)
2021-05-25 8:24 ` Avri Altman
2021-05-28 7:30 ` Avri Altman
2021-06-02 21:18 ` Asutosh Das (asd)
2021-05-25 1:40 ` Can Guo [this message]
2021-05-25 16:40 ` Bart Van Assche
2021-05-31 16:04 ` Bean Huo
2021-06-02 2:14 ` Can Guo
2021-06-03 0:18 ` Bart Van Assche
2021-06-03 2:54 ` Stanley Chu
2021-06-04 1:49 ` Can Guo
2021-06-17 2:49 ` Bart Van Assche
2021-06-23 2:04 ` Can Guo
2021-06-28 22:58 ` Bart Van Assche
2021-06-29 5:41 ` Can Guo
2021-07-01 15:57 ` Bart Van Assche
2021-05-24 8:36 ` [PATCH v1 3/3] scsi: ufs: Utilize Transfer Request List Completion Notification Register Can Guo
2021-05-31 16:05 ` Bean Huo
2021-06-03 2:54 ` Stanley Chu
2021-06-16 3:48 ` [PATCH v1 0/3] Optimize host lock on TR send/compl paths and utilize UTRLCNR Martin K. Petersen
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