From: Ira Weiny <ira.weiny@intel.com>
To: "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>,
"Tvrtko Ursulin" <tvrtko.ursulin@linux.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
Cc: Ira Weiny <ira.weiny@intel.com>,
"Fabio M . De Francesco" <fmdefrancesco@gmail.com>,
Zhenyu Wang <zhenyu.z.wang@intel.com>,
Zhao Liu <zhao1.liu@intel.com>
Subject: Re: [PATCH v2 9/9] drm/i915: Use kmap_local_page() in gem/i915_gem_execbuffer.c
Date: Thu, 30 Mar 2023 21:18:00 -0700 [thread overview]
Message-ID: <64265ef8725fe_375f7e294a@iweiny-mobl.notmuch> (raw)
In-Reply-To: <20230329073220.3982460-10-zhao1.liu@linux.intel.com>
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(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> index 9dce2957b4e5..805565edd148 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> @@ -1151,7 +1151,7 @@ static void reloc_cache_unmap(struct reloc_cache *cache)
>
> vaddr = unmask_page(cache->vaddr);
> if (cache->vaddr & KMAP)
> - kunmap_atomic(vaddr);
> + kunmap_local(vaddr);
In the cover letter you don't mention this unmap path. Rather you mention
only reloc_cache_reset().
After digging into this and considering these are kmap_atomic() calls I
_think_ what you have is ok. But I think I'd like to see the call paths
documented a bit more clearly. Or perhaps cleaned up a lot.
For example I see the following call possibility from a user ioctl. In
this trace I see 2 examples where something is unmapped first. I don't
understand why that is required? I would assume reloc_cache_unmap() and
reloc_kmap() are helpers called from somewhere else requiring a remapping
of the cache but I don't see it.
i915_gem_execbuffer2_ioctl()
eb_relocate_parse()
eb_relocate_parse_slow()
eb_relocate_vma_slow()
eb_relocate_entry()
reloc_cache_unmap()
kunmap_atomic() <=== HERE!
reloc_cache_remap()
kmap_atomic()
relocate_entry()
reloc_vaddr()
reloc_kmap()
kunmap_atomic() <== HERE!
kmap_atomic()
reloc_cache_reset()
kunmap_atomic()
Could these mappings be cleaned up a lot more? Perhaps by removing some
of the helper functions which AFAICT are left over from older versions of
the code?
Also as an aside I think it is really bad that eb_relocate_entry() returns
negative errors in a u64. Better to get the types right IMO.
Thanks for the series!
Ira
> else
> io_mapping_unmap_atomic((void __iomem *)vaddr);
> }
> @@ -1167,7 +1167,7 @@ static void reloc_cache_remap(struct reloc_cache *cache,
> if (cache->vaddr & KMAP) {
> struct page *page = i915_gem_object_get_page(obj, cache->page);
>
> - vaddr = kmap_atomic(page);
> + vaddr = kmap_local_page(page);
> cache->vaddr = unmask_flags(cache->vaddr) |
> (unsigned long)vaddr;
> } else {
> @@ -1197,7 +1197,7 @@ static void reloc_cache_reset(struct reloc_cache *cache, struct i915_execbuffer
> if (cache->vaddr & CLFLUSH_AFTER)
> mb();
>
> - kunmap_atomic(vaddr);
> + kunmap_local(vaddr);
> i915_gem_object_finish_access(obj);
> } else {
> struct i915_ggtt *ggtt = cache_to_ggtt(cache);
> @@ -1229,7 +1229,7 @@ static void *reloc_kmap(struct drm_i915_gem_object *obj,
> struct page *page;
>
> if (cache->vaddr) {
> - kunmap_atomic(unmask_page(cache->vaddr));
> + kunmap_local(unmask_page(cache->vaddr));
> } else {
> unsigned int flushes;
> int err;
> @@ -1251,7 +1251,7 @@ static void *reloc_kmap(struct drm_i915_gem_object *obj,
> if (!obj->mm.dirty)
> set_page_dirty(page);
>
> - vaddr = kmap_atomic(page);
> + vaddr = kmap_local_page(page);
> cache->vaddr = unmask_flags(cache->vaddr) | (unsigned long)vaddr;
> cache->page = pageno;
>
> --
> 2.34.1
>
next prev parent reply other threads:[~2023-03-31 4:21 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-29 7:32 [PATCH v2 0/9] drm/i915: Replace kmap_atomic() with kmap_local_page() Zhao Liu
2023-03-29 7:32 ` [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 ` [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 ` [PATCH v2 3/9] drm/i915: Use kmap_local_page() in gem/i915_gem_shmem.c Zhao Liu
2023-03-29 7:32 ` [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 ` [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 ` [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 ` [PATCH v2 7/9] drm/i915: Use memcpy_from_page() in gt/uc/intel_uc_fw.c Zhao Liu
2023-03-29 7:32 ` [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 ` [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 [this message]
2023-03-31 11:30 ` Tvrtko Ursulin
2023-03-31 15:32 ` Fabio M. De Francesco
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 16:03 ` [PATCH v2 0/9] drm/i915: Replace kmap_atomic() with kmap_local_page() Fabio M. De Francesco
2023-03-30 16:00 ` Zhao Liu
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=64265ef8725fe_375f7e294a@iweiny-mobl.notmuch \
--to=ira.weiny@intel.com \
--cc=airlied@gmail.com \
--cc=chris@chris-wilson.co.uk \
--cc=christian.koenig@amd.com \
--cc=daniel@ffwll.ch \
--cc=dri-devel@lists.freedesktop.org \
--cc=fmdefrancesco@gmail.com \
--cc=intel-gfx@lists.freedesktop.org \
--cc=jani.nikula@linux.intel.com \
--cc=joonas.lahtinen@linux.intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=maarten.lankhorst@linux.intel.com \
--cc=matthew.auld@intel.com \
--cc=nirmoy.das@intel.com \
--cc=rodrigo.vivi@intel.com \
--cc=thomas.hellstrom@linux.intel.com \
--cc=tvrtko.ursulin@linux.intel.com \
--cc=zhao1.liu@intel.com \
--cc=zhao1.liu@linux.intel.com \
--cc=zhenyu.z.wang@intel.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;
as well as URLs for NNTP newsgroup(s).