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{ "id": 2971, "url": "https://patchwork.libcamera.org/api/1.1/patches/2971/?format=api", "web_url": "https://patchwork.libcamera.org/patch/2971/", "project": { "id": 1, "url": "https://patchwork.libcamera.org/api/1.1/projects/1/?format=api", "name": "libcamera", "link_name": "libcamera", "list_id": "libcamera_core", "list_email": "libcamera-devel@lists.libcamera.org", "web_url": "", "scm_url": "", "webscm_url": "" }, "msgid": "<20200305203808.536050-8-niklas.soderlund@ragnatech.se>", "date": "2020-03-05T20:38:08", "name": "[libcamera-devel,v4,7/7] libcamera: V4L2BufferCache: Improve cache eviction strategy", "commit_ref": null, "pull_url": null, "state": "accepted", "archived": false, "hash": "73b49a30235a4535688cb33171e106ffc61726bb", "submitter": { "id": 5, "url": "https://patchwork.libcamera.org/api/1.1/people/5/?format=api", "name": "Niklas Söderlund", "email": "niklas.soderlund@ragnatech.se" }, "delegate": null, "mbox": "https://patchwork.libcamera.org/patch/2971/mbox/", "series": [ { "id": 702, "url": "https://patchwork.libcamera.org/api/1.1/series/702/?format=api", "web_url": "https://patchwork.libcamera.org/project/libcamera/list/?series=702", "date": "2020-03-05T20:38:01", "name": "libcamera: V4L2BufferCache: Improve cache eviction strategy", "version": 4, "mbox": "https://patchwork.libcamera.org/series/702/mbox/" } ], "comments": "https://patchwork.libcamera.org/api/patches/2971/comments/", "check": "pending", "checks": "https://patchwork.libcamera.org/api/patches/2971/checks/", "tags": {}, "headers": { "Return-Path": "<niklas.soderlund@ragnatech.se>", "Received": [ "from bin-mail-out-05.binero.net (bin-mail-out-05.binero.net\n\t[195.74.38.228])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id BB0F360427\n\tfor <libcamera-devel@lists.libcamera.org>;\n\tThu, 5 Mar 2020 21:38:24 +0100 (CET)", "from bismarck.berto.se (p4fca2392.dip0.t-ipconnect.de\n\t[79.202.35.146]) by bin-vsp-out-01.atm.binero.net (Halon) with ESMTPA\n\tid 420dd68b-5f21-11ea-9f85-005056917a89;\n\tThu, 05 Mar 2020 21:38:23 +0100 (CET)" ], "X-Halon-ID": "420dd68b-5f21-11ea-9f85-005056917a89", "Authorized-sender": "niklas@soderlund.pp.se", "From": "=?utf-8?q?Niklas_S=C3=B6derlund?= <niklas.soderlund@ragnatech.se>", "To": "libcamera-devel@lists.libcamera.org", "Date": "Thu, 5 Mar 2020 21:38:08 +0100", "Message-Id": "<20200305203808.536050-8-niklas.soderlund@ragnatech.se>", "X-Mailer": "git-send-email 2.25.1", "In-Reply-To": "<20200305203808.536050-1-niklas.soderlund@ragnatech.se>", "References": "<20200305203808.536050-1-niklas.soderlund@ragnatech.se>", "MIME-Version": "1.0", "Content-Type": "text/plain; charset=UTF-8", "Content-Transfer-Encoding": "8bit", "Subject": "[libcamera-devel] [PATCH v4 7/7] libcamera: V4L2BufferCache:\n\tImprove cache eviction strategy", "X-BeenThere": "libcamera-devel@lists.libcamera.org", "X-Mailman-Version": "2.1.29", "Precedence": "list", "List-Id": "<libcamera-devel.lists.libcamera.org>", "List-Unsubscribe": "<https://lists.libcamera.org/options/libcamera-devel>,\n\t<mailto:libcamera-devel-request@lists.libcamera.org?subject=unsubscribe>", "List-Archive": "<https://lists.libcamera.org/pipermail/libcamera-devel/>", "List-Post": "<mailto:libcamera-devel@lists.libcamera.org>", "List-Help": "<mailto:libcamera-devel-request@lists.libcamera.org?subject=help>", "List-Subscribe": "<https://lists.libcamera.org/listinfo/libcamera-devel>,\n\t<mailto:libcamera-devel-request@lists.libcamera.org?subject=subscribe>", "X-List-Received-Date": "Thu, 05 Mar 2020 20:38:25 -0000" }, "content": "The strategy used to find a free cache entry in the first implementation\nwas not the smartest, it picked the first free entry. This lead to\nunwanted performance issues as the cache was not used as good as it\ncould for imported buffers.\n\nImprove this by adding a last usage sequence number to the cache entries\nand change the eviction strategy to use the oldest free entry instead of\nthe first one it finds.\n\nSigned-off-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>\nReviewed-by: Naushir Patuck <naush@raspberrypi.com>\nReviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>\n---\n* Changes since v3\n- Group C++ header includes.\n- s/UINT32_MAX/UINT64_MAX/\n- Use std::memory_order_acq_rel instead of std::memory_order_seq_cst\n order to fetch_add() of the atomic sequence number.\n* Changes since v2\n- Use a sequence number instead of timestamp to judge age of a cached\n entry.\n---\n src/libcamera/include/v4l2_videodevice.h | 7 +++++--\n src/libcamera/v4l2_videodevice.cpp | 23 +++++++++++++++--------\n 2 files changed, 20 insertions(+), 10 deletions(-)", "diff": "diff --git a/src/libcamera/include/v4l2_videodevice.h b/src/libcamera/include/v4l2_videodevice.h\nindex 359b366454e4e782..04802012d5315d67 100644\n--- a/src/libcamera/include/v4l2_videodevice.h\n+++ b/src/libcamera/include/v4l2_videodevice.h\n@@ -7,11 +7,12 @@\n #ifndef __LIBCAMERA_V4L2_VIDEODEVICE_H__\n #define __LIBCAMERA_V4L2_VIDEODEVICE_H__\n \n+#include <atomic>\n+#include <memory>\n #include <string>\n #include <vector>\n \n #include <linux/videodev2.h>\n-#include <memory>\n \n #include <libcamera/buffer.h>\n #include <libcamera/geometry.h>\n@@ -120,11 +121,12 @@ private:\n \t{\n \tpublic:\n \t\tEntry();\n-\t\tEntry(bool free, const FrameBuffer &buffer);\n+\t\tEntry(bool free, uint64_t lastUsed, const FrameBuffer &buffer);\n \n \t\tbool operator==(const FrameBuffer &buffer) const;\n \n \t\tbool free;\n+\t\tuint64_t lastUsed;\n \n \tprivate:\n \t\tstruct Plane {\n@@ -140,6 +142,7 @@ private:\n \t\tstd::vector<Plane> planes_;\n \t};\n \n+\tstd::atomic_uint64_t lastUsedCounter_;\n \tstd::vector<Entry> cache_;\n \t/* \\todo Expose the miss counter through an instrumentation API. */\n \tunsigned int missCounter_;\ndiff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp\nindex c495de85f26efe14..ca0d147f5fc1ea58 100644\n--- a/src/libcamera/v4l2_videodevice.cpp\n+++ b/src/libcamera/v4l2_videodevice.cpp\n@@ -162,7 +162,7 @@ LOG_DECLARE_CATEGORY(V4L2)\n * buffer import, with buffers added to the cache as they are queued.\n */\n V4L2BufferCache::V4L2BufferCache(unsigned int numEntries)\n-\t: missCounter_(0)\n+\t: lastUsedCounter_(1), missCounter_(0)\n {\n \tcache_.resize(numEntries);\n }\n@@ -176,10 +176,12 @@ V4L2BufferCache::V4L2BufferCache(unsigned int numEntries)\n * allocated.\n */\n V4L2BufferCache::V4L2BufferCache(const std::vector<std::unique_ptr<FrameBuffer>> &buffers)\n-\t: missCounter_(0)\n+\t: lastUsedCounter_(1), missCounter_(0)\n {\n \tfor (const std::unique_ptr<FrameBuffer> &buffer : buffers)\n-\t\tcache_.emplace_back(true, buffer->planes());\n+\t\tcache_.emplace_back(true,\n+\t\t\t\t lastUsedCounter_.fetch_add(1, std::memory_order_acq_rel),\n+\t\t\t\t buffer->planes());\n }\n \n V4L2BufferCache::~V4L2BufferCache()\n@@ -205,6 +207,7 @@ int V4L2BufferCache::get(const FrameBuffer &buffer)\n {\n \tbool hit = false;\n \tint use = -1;\n+\tuint64_t oldest = UINT64_MAX;\n \n \tfor (unsigned int index = 0; index < cache_.size(); index++) {\n \t\tconst Entry &entry = cache_[index];\n@@ -219,8 +222,10 @@ int V4L2BufferCache::get(const FrameBuffer &buffer)\n \t\t\tbreak;\n \t\t}\n \n-\t\tif (use < 0)\n+\t\tif (entry.lastUsed < oldest) {\n \t\t\tuse = index;\n+\t\t\toldest = entry.lastUsed;\n+\t\t}\n \t}\n \n \tif (!hit)\n@@ -229,7 +234,9 @@ int V4L2BufferCache::get(const FrameBuffer &buffer)\n \tif (use < 0)\n \t\treturn -ENOENT;\n \n-\tcache_[use] = Entry(false, buffer);\n+\tcache_[use] = Entry(false,\n+\t\t\t lastUsedCounter_.fetch_add(1, std::memory_order_acq_rel),\n+\t\t\t buffer);\n \n \treturn use;\n }\n@@ -245,12 +252,12 @@ void V4L2BufferCache::put(unsigned int index)\n }\n \n V4L2BufferCache::Entry::Entry()\n-\t: free(true)\n+\t: free(true), lastUsed(0)\n {\n }\n \n-V4L2BufferCache::Entry::Entry(bool free, const FrameBuffer &buffer)\n-\t: free(free)\n+V4L2BufferCache::Entry::Entry(bool free, uint64_t lastUsed, const FrameBuffer &buffer)\n+\t: free(free), lastUsed(lastUsed)\n {\n \tfor (const FrameBuffer::Plane &plane : buffer.planes())\n \t\tplanes_.emplace_back(plane);\n", "prefixes": [ "libcamera-devel", "v4", "7/7" ] }