Re: [PATCH] drm/msm/dpu: Add missing safe_lut_tbl in sc8280xp catalog

From: Rob Clark <robdclark@gmail.com>
To: Johan Hovold <johan@kernel.org>
Cc: Bjorn Andersson <quic_bjorande@quicinc.com>,
	Abhinav Kumar <quic_abhinavk@quicinc.com>,
	Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
	Sean Paul <sean@poorly.run>,
	Marijn Suijten <marijn.suijten@somainline.org>,
	David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
	Bjorn Andersson <andersson@kernel.org>,
	Kuogee Hsieh <quic_khsieh@quicinc.com>,
	linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org,
	freedreno@lists.freedesktop.org, linux-kernel@vger.kernel.org,
	stable@vger.kernel.org, Doug Anderson <dianders@chromium.org>,
	Rob Clark <robdclark@chromium.org>
Subject: Re: [PATCH] drm/msm/dpu: Add missing safe_lut_tbl in sc8280xp catalog
Date: Tue, 31 Oct 2023 05:47:50 -0700	[thread overview]
Message-ID: <CAF6AEGs9PLiCZdJ-g42-bE6f9yMR6cMyKRdWOY5m799vF9o4SQ@mail.gmail.com> (raw)
In-Reply-To: <ZUD0lhStirf8IN8-@hovoldconsulting.com>

On Tue, Oct 31, 2023 at 5:35 AM Johan Hovold <johan@kernel.org> wrote:
>
> On Mon, Oct 30, 2023 at 04:23:20PM -0700, Bjorn Andersson wrote:
> > During USB transfers on the SC8280XP __arm_smmu_tlb_sync() is seen to
> > typically take 1-2ms to complete. As expected this results in poor
> > performance, something that has been mitigated by proposing running the
> > iommu in non-strict mode (boot with iommu.strict=0).
> >
> > This turns out to be related to the SAFE logic, and programming the QOS
> > SAFE values in the DPU (per suggestion from Rob and Doug) reduces the
> > TLB sync time to below 10us, which means significant less time spent
> > with interrupts disabled and a significant boost in throughput.
>
> I ran some tests with a gigabit ethernet adapter to get an idea of how
> this performs in comparison to using lazy iommu mode ("non-strict"):
>
>                 6.6     6.6-lazy        6.6-dpu         6.6-dpu-lazy
> iperf3 recv     114     941             941             941             MBit/s
> iperf3 send     124     891             703             940             MBit/s
>
> scp recv        14.6    110             110             111             MB/s
> scp send        12.5    98.9            91.5            110             MB/s
>
> This patch in itself indeed improves things quite a bit, but there is
> still some performance that can be gained by using lazy iommu mode.
>
> Notably, lazy mode with this patch applied appears to saturate the link
> in both directions.

Maybe there is still room for SoC specific udev rules so dma masters
without firmware can be configured as "lazy", ie. like:

https://chromium.googlesource.com/chromiumos/overlays/board-overlays/+/refs/heads/main/baseboard-trogdor/chromeos-base/chromeos-bsp-baseboard-trogdor/files/98-qcom-nonstrict-iommu.rules

BR,
-R

> Tested-by: Johan Hovold <johan+linaro@kernel.org>
>
> Johan