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[87.19.108.254]) by smtp.gmail.com with ESMTPSA id y12-20020a5d470c000000b002c70ce264bfsm10238018wrq.76.2023.04.17.03.39.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Apr 2023 03:39:01 -0700 (PDT) From: "Fabio M. De Francesco" To: Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , David Airlie , Daniel Vetter , Matt Roper , John Harrison , Daniele Ceraolo Spurio , Chris Wilson , intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Cc: "Fabio M. De Francesco" , Ira Weiny Subject: [PATCH v2 1/3] drm/i915: Replace kmap() with kmap_local_page() Date: Mon, 17 Apr 2023 12:38:52 +0200 Message-Id: <20230417103854.23333-2-fmdefrancesco@gmail.com> X-Mailer: git-send-email 2.40.0 In-Reply-To: <20230417103854.23333-1-fmdefrancesco@gmail.com> References: <20230417103854.23333-1-fmdefrancesco@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org kmap() has been deprecated in favor of kmap_local_page(). There are two main problems with kmap(): (1) It comes with an overhead as mapping space is restricted and protected by a global lock for synchronization and (2) it also requires global TLB invalidation when the kmap=E2=80=99s pool wraps and it might block when the mapping space is fully utilized until a slot becomes available. With kmap_local_page() the mappings are per thread, CPU local, can take page faults, and can be called from any context (including interrupts). It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore, the tasks can be preempted and, when they are scheduled to run again, the kernel virtual addresses are restored and are still valid. Obviously, thread locality implies that the kernel voirtual addresses are valid only in the context of the callers. kmap_local_page() use in i915_gem.c doesn't break the above-mentioned constraint, so it should be preferred to kmap(). Therefore, replace kmap() with kmap_local_page() in i915_gem.c Suggested-by: Ira Weiny Signed-off-by: Fabio M. De Francesco --- drivers/gpu/drm/i915/i915_gem.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_ge= m.c index 35950fa91406..c35248555e42 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -212,14 +212,14 @@ shmem_pread(struct page *page, int offset, int len, c= har __user *user_data, char *vaddr; int ret; - vaddr =3D kmap(page); + vaddr =3D kmap_local_page(page); if (needs_clflush) drm_clflush_virt_range(vaddr + offset, len); ret =3D __copy_to_user(user_data, vaddr + offset, len); - kunmap(page); + kunmap_local(vaddr); return ret ? -EFAULT : 0; } @@ -643,7 +643,7 @@ shmem_pwrite(struct page *page, int offset, int len, ch= ar __user *user_data, char *vaddr; int ret; - vaddr =3D kmap(page); + vaddr =3D kmap_local_page(page); if (needs_clflush_before) drm_clflush_virt_range(vaddr + offset, len); @@ -652,7 +652,7 @@ shmem_pwrite(struct page *page, int offset, int len, ch= ar __user *user_data, if (!ret && needs_clflush_after) drm_clflush_virt_range(vaddr + offset, len); - kunmap(page); + kunmap_local(vaddr); return ret ? -EFAULT : 0; } -- 2.40.0