From: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To: "Ira Weiny" <ira.weiny@intel.com>,
"Zhao Liu" <zhao1.liu@linux.intel.com>,
"Jani Nikula" <jani.nikula@linux.intel.com>,
"Joonas Lahtinen" <joonas.lahtinen@linux.intel.com>,
"Rodrigo Vivi" <rodrigo.vivi@intel.com>,
"David Airlie" <airlied@gmail.com>,
"Daniel Vetter" <daniel@ffwll.ch>,
"Matthew Auld" <matthew.auld@intel.com>,
"Thomas Hellström" <thomas.hellstrom@linux.intel.com>,
"Nirmoy Das" <nirmoy.das@intel.com>,
"Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
"Chris Wilson" <chris@chris-wilson.co.uk>,
"Christian König" <christian.koenig@amd.com>,
intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
linux-kernel@vger.kernel.org,
"Tvrtko Ursulin" <tvrtko.ursulin@linux.intel.com>
Cc: Zhao Liu <zhao1.liu@intel.com>, Zhenyu Wang <zhenyu.z.wang@intel.com>
Subject: Re: [Intel-gfx] [PATCH v2 9/9] drm/i915: Use kmap_local_page() in gem/i915_gem_execbuffer.c
Date: Fri, 31 Mar 2023 17:32:17 +0200 [thread overview]
Message-ID: <2177327.1BCLMh4Saa@suse> (raw)
In-Reply-To: <fdc8a470-1e6b-815d-e367-a9df1b0b14dd@linux.intel.com>
On venerdì 31 marzo 2023 13:30:20 CEST Tvrtko Ursulin wrote:
> On 31/03/2023 05:18, Ira Weiny wrote:
> > Zhao Liu wrote:
> >> From: Zhao Liu <zhao1.liu@intel.com>
> >>
> >> The use of kmap_atomic() is being deprecated in favor of
> >> kmap_local_page()[1], and this patch converts the calls from
> >> kmap_atomic() to kmap_local_page().
> >>
> >> The main difference between atomic and local mappings is that local
> >> mappings doesn't disable page faults or preemption (the preemption is
> >> disabled for !PREEMPT_RT case, otherwise it only disables migration).
> >>
> >> With kmap_local_page(), we can avoid the often unwanted side effect of
> >> unnecessary page faults and preemption disables.
> >>
> >> In i915_gem_execbuffer.c, eb->reloc_cache.vaddr is mapped by
> >> kmap_atomic() in eb_relocate_entry(), and is unmapped by
> >> kunmap_atomic() in reloc_cache_reset().
> >
> > First off thanks for the series and sticking with this. That said this
> > patch kind of threw me for a loop because tracing the map/unmap calls did
> > not make sense to me. See below.
> >
> >> And this mapping/unmapping occurs in two places: one is in
> >> eb_relocate_vma(), and another is in eb_relocate_vma_slow().
> >>
> >> The function eb_relocate_vma() or eb_relocate_vma_slow() doesn't
> >> need to disable pagefaults and preemption during the above mapping/
> >> unmapping.
> >>
> >> So it can simply use kmap_local_page() / kunmap_local() that can
> >> instead do the mapping / unmapping regardless of the context.
> >>
> >> Convert the calls of kmap_atomic() / kunmap_atomic() to
> >> kmap_local_page() / kunmap_local().
> >>
> >> [1]:
> >> https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com
> >>
> >> v2: No code change since v1. Added description of the motivation of
> >>
> >> using kmap_local_page() and "Suggested-by" tag of Fabio.
> >>
> >> Suggested-by: Ira Weiny <ira.weiny@intel.com>
> >> Suggested-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> >> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> >> ---
> >>
> >> Suggested by credits:
> >> Ira: Referred to his task document, review comments.
> >> Fabio: Referred to his boiler plate commit message and his description
> >>
> >> about why kmap_local_page() should be preferred.
> >>
> >> ---
> >>
> >> drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 10 +++++-----
> >> 1 file changed, 5 insertions(+), 5 deletions(-)
> >>
[snip]
> However I am unsure if disabling pagefaulting is needed or not. Thomas,
> Matt, being the last to touch this area, perhaps you could have a look?
> Because I notice we have a fallback iomap path which still uses
> io_mapping_map_atomic_wc. So if kmap_atomic to kmap_local conversion is
> safe, does the iomap side also needs converting to
> io_mapping_map_local_wc? Or they have separate requirements?
AFAIK, the requirements for io_mapping_map_local_wc() are the same as for
kmap_local_page(): the kernel virtual address is _only_ valid in the caller
context, and map/unmap nesting must be done in stack-based ordering (LIFO).
I think a follow up patch could safely switch to io_mapping_map_local_wc() /
io_mapping_unmap_local_wc since the address is local to context.
However, not being an expert, reading your note now I suspect that I'm missing
something. Can I ask why you think that page-faults disabling might be
necessary?
Thanks,
Fabio
> Regards,
>
> Tvrtko
next prev parent reply other threads:[~2023-03-31 15:32 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-29 7:32 [Intel-gfx] [PATCH v2 0/9] drm/i915: Replace kmap_atomic() with kmap_local_page() Zhao Liu
2023-03-29 7:32 ` [Intel-gfx] [PATCH v2 1/9] drm/i915: Use kmap_local_page() in gem/i915_gem_object.c Zhao Liu
2023-03-30 21:56 ` Ira Weiny
2023-03-29 7:32 ` [Intel-gfx] [PATCH v2 2/9] drm/i915: Use memcpy_[from/to]_page() in gem/i915_gem_pyhs.c Zhao Liu
2023-03-30 23:01 ` Ira Weiny
2023-03-29 7:32 ` [Intel-gfx] [PATCH v2 3/9] drm/i915: Use kmap_local_page() in gem/i915_gem_shmem.c Zhao Liu
2023-03-29 7:32 ` [Intel-gfx] [PATCH v2 4/9] drm/i915: Use kmap_local_page() in gem/selftests/huge_pages.c Zhao Liu
2023-03-31 3:04 ` Ira Weiny
2023-03-29 7:32 ` [Intel-gfx] [PATCH v2 5/9] drm/i915: Use kmap_local_page() in gem/selftests/i915_gem_coherency.c Zhao Liu
2023-03-31 3:07 ` Ira Weiny
2023-03-29 7:32 ` [Intel-gfx] [PATCH v2 6/9] drm/i915: Use kmap_local_page() in gem/selftests/i915_gem_context.c Zhao Liu
2023-03-31 3:33 ` Ira Weiny
2023-03-31 8:05 ` Tvrtko Ursulin
2023-03-29 7:32 ` [Intel-gfx] [PATCH v2 7/9] drm/i915: Use memcpy_from_page() in gt/uc/intel_uc_fw.c Zhao Liu
2023-03-29 7:32 ` [Intel-gfx] [PATCH v2 8/9] drm/i915: Use kmap_local_page() in i915_cmd_parser.c Zhao Liu
2023-03-31 3:36 ` Ira Weiny
2023-03-29 7:32 ` [Intel-gfx] [PATCH v2 9/9] drm/i915: Use kmap_local_page() in gem/i915_gem_execbuffer.c Zhao Liu
2023-03-31 4:18 ` Ira Weiny
2023-03-31 11:30 ` Tvrtko Ursulin
2023-03-31 15:32 ` Fabio M. De Francesco [this message]
2023-04-10 9:08 ` Zhao Liu
2023-04-12 15:45 ` Tvrtko Ursulin
2023-04-14 10:45 ` Zhao Liu
2023-04-17 11:24 ` Tvrtko Ursulin
2023-04-17 14:53 ` Rodrigo Vivi
2023-10-18 16:19 ` Zhao Liu
2023-10-19 9:02 ` Tvrtko Ursulin
2023-03-29 8:17 ` [Intel-gfx] ✗ Fi.CI.CHECKPATCH: warning for drm/i915: Replace kmap_atomic() with kmap_local_page() Patchwork
2023-03-29 8:18 ` [Intel-gfx] ✗ Fi.CI.SPARSE: " Patchwork
2023-03-29 8:37 ` [Intel-gfx] ✓ Fi.CI.BAT: success " Patchwork
2023-03-29 16:03 ` [Intel-gfx] [PATCH v2 0/9] " Fabio M. De Francesco
2023-03-30 16:00 ` Zhao Liu
2023-03-29 19:51 ` [Intel-gfx] ✓ Fi.CI.IGT: success for " Patchwork
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