linux-kernel - Re: [PREEMPT_RT PATCH 2/3] i915: convert all irq

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Date:   Tue, 3 Sep 2019 15:09:30 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Clark Williams <clark.williams@...il.com>
Cc:     bigeasy@...utronix.com, tglx@...utronix.com,
        linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PREEMPT_RT PATCH 2/3] i915: convert all irq_locks spinlocks to
 raw spinlocks

On 2019-09-03 10:03:35 [+0200], To Clark Williams wrote:
> anything in a brief test. What I saw however is that switching to
> fullscreen while playing a video gives me ~0.5 to ~2ms latency. This is
> has nothing to do with this change, I have to dig deeper… It might be
> one of the preempt_disable() section I just noticed.
> I would prefer to keep the lock non-raw unless there is actual need for
> it.

That latency spike is caused by the iommu, qi_submit_sync() to be exact.
Without the iomm I don't see much difference between the two patches…
 
Sebastian