On 17/05/2024 11:39, Thomas Zimmermann wrote:
Hi,
just nits below.
Am 16.05.24 um 18:17 schrieb Jocelyn Falempe:
Unfortunately, the G200 ioburst workaround doesn't work on some servers
like Dell poweredge XR11, XR5610, or HPE XL260
In this case completely disabling WC is the only option to achieve
low-latency.
So this adds a new Kconfig option, to disable WC mapping of the G200
The formatting look off. Maybe make this one single paragraph.
Ok,
No comma after 'option'.
Ok,
Signed-off-by: Jocelyn Falempe <jfalempe@xxxxxxxxxx>
---
drivers/gpu/drm/mgag200/Kconfig | 10 ++++++++++
drivers/gpu/drm/mgag200/mgag200_drv.c | 7 +++++++
2 files changed, 17 insertions(+)
diff --git a/drivers/gpu/drm/mgag200/Kconfig
b/drivers/gpu/drm/mgag200/Kconfig
index b28c5e4828f47..73ab5730b74d9 100644
--- a/drivers/gpu/drm/mgag200/Kconfig
+++ b/drivers/gpu/drm/mgag200/Kconfig
@@ -11,3 +11,13 @@ config DRM_MGAG200
MGA G200 desktop chips and the server variants. It requires 0.3.0
of the modesetting userspace driver, and a version of mga driver
that will fail on KMS enabled devices.
+
+config DRM_MGAG200_DISABLE_WRITECOMBINE
+ bool "Disable Write Combine mapping of VRAM"
+ depends on DRM_MGAG200 && PREEMPT_RT
+ help
+ The VRAM of the G200 is mapped with Write-Combine, to improve
No comma after Write-Combine
Ok
+ performances. However this increases the system latency a lot,
even
Just say "This can interfere with real-time tasks; even if they are
running on other CPU cores then the graphics output."
Ok
+ for realtime tasks running on other CPU cores. Typically 40us-80us
+ latencies are measured with hwlat when Write Combine is enabled.
Leave out the next sentence: "Typically ..." The measureed numbers
depend on the hardware and everyone is encouraged to test on their own
system. You could mention the numbers in the commit description, as you
already mention the affected systems there.
Ok
+ Recommended if you run realtime tasks on a server with a Matrox
G200.
I still think that we should not encourage anyone to use this option.
Maybe say "Enable this option only if you run..."
Agreed, I will change this.
\ No newline at end of file
diff --git a/drivers/gpu/drm/mgag200/mgag200_drv.c
b/drivers/gpu/drm/mgag200/mgag200_drv.c
index 3883f25ca4d8b..7461e3f984eff 100644
--- a/drivers/gpu/drm/mgag200/mgag200_drv.c
+++ b/drivers/gpu/drm/mgag200/mgag200_drv.c
@@ -146,12 +146,19 @@ int mgag200_device_preinit(struct mga_device *mdev)
}
mdev->vram_res = res;
+#if defined(CONFIG_DRM_MGAG200_DISABLE_WRITECOMBINE)
+ drm_info(dev, "Disable Write Combine\n");
I would not print this drm_info() here. The user has selected the config
option, so they should know what happens. It's also listed in /proc/mtrr
IIRC.
Sure, I can remove the drm_info().
Thanks for the review, I will send a v2 shortly.
Best regards
Thomas
+ mdev->vram = devm_ioremap(dev->dev, res->start, resource_size(res));
+ if (!mdev->vram)
+ return -ENOMEM;
+#else
mdev->vram = devm_ioremap_wc(dev->dev, res->start,
resource_size(res));
if (!mdev->vram)
return -ENOMEM;
/* Don't fail on errors, but performance might be reduced. */
devm_arch_phys_wc_add(dev->dev, res->start, resource_size(res));
+#endif
return 0;
}
