From: Will Deacon <will@kernel.org>
To: Jacob Pan <jacob.pan@linux.microsoft.com>
Cc: linux-kernel@vger.kernel.org,
"iommu@lists.linux.dev" <iommu@lists.linux.dev>,
Joerg Roedel <joro@8bytes.org>,
Mostafa Saleh <smostafa@google.com>,
Jason Gunthorpe <jgg@nvidia.com>,
Robin Murphy <robin.murphy@arm.com>,
Nicolin Chen <nicolinc@nvidia.com>,
Zhang Yu <zhangyu1@linux.microsoft.com>,
Jean Philippe-Brucker <jean-philippe@linaro.org>,
Alexander Grest <Alexander.Grest@microsoft.com>
Subject: Re: [PATCH v4 2/2] iommu/arm-smmu-v3: Improve CMDQ lock fairness and efficiency
Date: Wed, 10 Dec 2025 12:11:47 +0900 [thread overview]
Message-ID: <aTjk89lJFc3sNTN_@google.com> (raw)
In-Reply-To: <20251130145236.0000009d@linux.microsoft.com>
On Sun, Nov 30, 2025 at 02:52:36PM -0800, Jacob Pan wrote:
> On Tue, 25 Nov 2025 17:18:57 +0000
> Will Deacon <will@kernel.org> wrote:
> > That aside, doesn't this introduce a new fairness issue in that a
> > steady stream of shared lockers will starve somebody trying to take
> > the lock in exclusive state?
> >
> I don't think this change will starve exclusive lockers in the
> current code flow since new shared locker must acquire exclusive locker
> first while polling for available queue spaces.
Looking at this again, we already have the same starvation problem in
that the lockword has to hit zero for the exclusive locker to succeed.
So my initial worry was unfounded.
Will
next prev parent reply other threads:[~2025-12-10 3:11 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-14 17:17 [PATCH v4 0/2] SMMU v3 CMDQ fix and improvement Jacob Pan
2025-11-14 17:17 ` [PATCH v4 1/2] iommu/arm-smmu-v3: Fix CMDQ timeout warning Jacob Pan
2025-11-14 18:29 ` Nicolin Chen
2025-11-25 17:19 ` Will Deacon
2025-11-30 23:06 ` Jacob Pan
2025-12-01 19:57 ` Robin Murphy
2025-12-01 21:49 ` Jacob Pan
2025-12-01 17:42 ` Jacob Pan
2025-11-14 17:17 ` [PATCH v4 2/2] iommu/arm-smmu-v3: Improve CMDQ lock fairness and efficiency Jacob Pan
2025-11-25 17:18 ` Will Deacon
2025-11-30 22:52 ` Jacob Pan
2025-12-10 3:11 ` Will Deacon [this message]
2025-11-20 17:10 ` [PATCH v4 0/2] SMMU v3 CMDQ fix and improvement Jacob Pan
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=aTjk89lJFc3sNTN_@google.com \
--to=will@kernel.org \
--cc=Alexander.Grest@microsoft.com \
--cc=iommu@lists.linux.dev \
--cc=jacob.pan@linux.microsoft.com \
--cc=jean-philippe@linaro.org \
--cc=jgg@nvidia.com \
--cc=joro@8bytes.org \
--cc=linux-kernel@vger.kernel.org \
--cc=nicolinc@nvidia.com \
--cc=robin.murphy@arm.com \
--cc=smostafa@google.com \
--cc=zhangyu1@linux.microsoft.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox