[{"id":38302,"web_url":"https://patchwork.libcamera.org/comment/38302/","msgid":"<851pi9c660.fsf@mzamazal-thinkpadp1gen7.tpbc.csb>","date":"2026-02-25T13:19:03","subject":"Re: [PATCH v3 3/4] software_isp: debayer_cpu: Add multi-threading\n\tsupport","submitter":{"id":177,"url":"https://patchwork.libcamera.org/api/people/177/","name":"Milan Zamazal","email":"mzamazal@redhat.com"},"content":"Hi Hans,\n\nthank you for the update.\n\nHans de Goede writes:\n\n> Add CPU soft ISP multi-threading support.\n>\n> Benchmark results for the Arduino Uno-Q with a weak CPU which is good for\n> performance testing, all numbers with an IMX219 running at\n> 3280x2464 -> 3272x2464:\n>\n> 1 thread : 147ms / frame, ~6.5 fps\n> 2 threads: 80ms / frame, ~12.5 fps\n> 3 threads: 65ms / frame, ~15 fps\n>\n> Adding a 4th thread does not improve performance.\n>\n> Signed-off-by: Hans de Goede \n> ---\n> Changes in v3:\n> - Adjust for DebayerCpuThread now inheriting from Thread\n> - Use for (auto &thread : threads_)\n>\n> Changes in v2:\n> - Adjust to use the new DebayerCpuThread class introduced in the v2 patch-series\n> - Re-use threads instead of starting new threads every frame\n> ---\n> src/libcamera/software_isp/debayer_cpu.cpp | 45 ++++++++++++++++++++--\n> src/libcamera/software_isp/debayer_cpu.h | 6 +++\n> 2 files changed, 48 insertions(+), 3 deletions(-)\n>\n> diff --git a/src/libcamera/software_isp/debayer_cpu.cpp b/src/libcamera/software_isp/debayer_cpu.cpp\n> index 36b7881b..cf16f00b 100644\n> --- a/src/libcamera/software_isp/debayer_cpu.cpp\n> +++ b/src/libcamera/software_isp/debayer_cpu.cpp\n> @@ -73,6 +73,7 @@ DebayerCpuThread::DebayerCpuThread(DebayerCpu *debayer, unsigned int threadIndex\n> \t debayer_(debayer), threadIndex_(threadIndex),\n> \t enableInputMemcpy_(enableInputMemcpy)\n> {\n> +\tmoveToThread(this);\n> }\n> \n> /**\n> @@ -104,8 +105,10 @@ DebayerCpu::DebayerCpu(std::unique_ptr stats, const GlobalConfigurat\n> \tbool enableInputMemcpy =\n> \t\tconfiguration.option({ \"software_isp\", \"copy_input_buffer\" }).value_or(true);\n> \n> -\t/* Just one thread object for now, which will be called inline rather than async */\n> -\tthreads_.resize(1);\n> +\tunsigned int threadCount =\n> +\t\tconfiguration.option({ \"software_isp\", \"threads\" }).value_or(2);\n\nThe configuration option should be documented in\nruntime_configuration.rst.\n\nAlso, I wouldn't mind making the default value more prominently visible,\nlike mentioning it in the documentation and/or defining it as a named\nconstant.\n\n> +\tthreadCount = std::clamp(threadCount, 1u, 8u);\n> +\tthreads_.resize(threadCount);\n> \n> \tfor (unsigned int i = 0; i < threads_.size(); i++)\n> \t\tthreads_[i] = std::make_unique(this, i, enableInputMemcpy);\n> @@ -743,6 +746,11 @@ void DebayerCpuThread::process(uint32_t frame, const uint8_t *src, uint8_t *dst)\n> \t\tprocess2(frame, src, dst);\n> \telse\n> \t\tprocess4(frame, src, dst);\n> +\n> +\tdebayer_->workPendingMutex_.lock();\n> +\tdebayer_->workPending_ &= ~(1 << threadIndex_);\n> +\tdebayer_->workPendingMutex_.unlock();\n> +\tdebayer_->workPendingCv_.notify_one();\n> }\n> \n> void DebayerCpuThread::process2(uint32_t frame, const uint8_t *src, uint8_t *dst)\n> @@ -982,7 +990,21 @@ void DebayerCpu::process(uint32_t frame, FrameBuffer *input, FrameBuffer *output\n> \n> \tstats_->startFrame(frame);\n> \n> -\tthreads_[0]->process(frame, in.planes()[0].data(), out.planes()[0].data());\n> +\tworkPendingMutex_.lock();\n> +\tworkPending_ = (1 << threads_.size()) - 1;\n> +\tworkPendingMutex_.unlock();\n> +\n> +\tfor (auto &thread : threads_)\n> +\t\tthread->invokeMethod(&DebayerCpuThread::process,\n> +\t\t\t\t ConnectionTypeQueued, frame,\n> +\t\t\t\t in.planes()[0].data(), out.planes()[0].data());\n> +\n> +\t{\n> +\t\tMutexLocker locker(workPendingMutex_);\n> +\t\tworkPendingCv_.wait(locker, [&]() LIBCAMERA_TSA_REQUIRES(workPendingMutex_) {\n> +\t\t\treturn workPending_ == 0;\n> +\t\t});\n> +\t}\n> \n> \tmetadata.planes()[0].bytesused = out.planes()[0].size();\n> \n> @@ -1001,6 +1023,23 @@ void DebayerCpu::process(uint32_t frame, FrameBuffer *input, FrameBuffer *output\n> \tinputBufferReady.emit(input);\n> }\n> \n> +int DebayerCpu::start()\n> +{\n> +\tfor (auto &thread : threads_)\n> +\t\tthread->start();\n> +\n> +\treturn 0;\n> +}\n> +\n> +void DebayerCpu::stop()\n> +{\n> +\tfor (auto &thread : threads_)\n> +\t\tthread->exit();\n> +\n> +\tfor (auto &thread : threads_)\n> +\t\tthread->wait();\n> +}\n> +\n> SizeRange DebayerCpu::sizes(PixelFormat inputFormat, const Size &inputSize)\n> {\n> \tSize patternSize = this->patternSize(inputFormat);\n> diff --git a/src/libcamera/software_isp/debayer_cpu.h b/src/libcamera/software_isp/debayer_cpu.h\n> index 1074bc9c..eb52f101 100644\n> --- a/src/libcamera/software_isp/debayer_cpu.h\n> +++ b/src/libcamera/software_isp/debayer_cpu.h\n> @@ -16,6 +16,7 @@\n> #include \n> \n> #include \n> +#include \n> \n> #include \"libcamera/internal/bayer_format.h\"\n> #include \"libcamera/internal/global_configuration.h\"\n> @@ -41,6 +42,8 @@ public:\n> \tstd::tuple\n> \tstrideAndFrameSize(const PixelFormat &outputFormat, const Size &size);\n> \tvoid process(uint32_t frame, FrameBuffer *input, FrameBuffer *output, const DebayerParams ¶ms);\n> +\tint start();\n> +\tvoid stop();\n> \tSizeRange sizes(PixelFormat inputFormat, const Size &inputSize);\n> \tconst SharedFD &getStatsFD() { return stats_->getStatsFD(); }\n> \n> @@ -147,6 +150,9 @@ private:\n> \tstd::unique_ptr stats_;\n> \tunsigned int xShift_; /* Offset of 0/1 applied to window_.x */\n> \n> +\tunsigned int workPending_ LIBCAMERA_TSA_GUARDED_BY(workPendingMutex_);\n> +\tMutex workPendingMutex_;\n> +\tConditionVariable workPendingCv_;\n> \tstd::vector>threads_;\n> };","headers":{"Return-Path":"","X-Original-To":"parsemail@patchwork.libcamera.org","Delivered-To":"parsemail@patchwork.libcamera.org","Received":["from lancelot.ideasonboard.com (lancelot.ideasonboard.com\n\t[92.243.16.209])\n\tby patchwork.libcamera.org (Postfix) with ESMTPS id 66424C3237\n\tfor ;\n\tWed, 25 Feb 2026 13:19:13 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 5ED42622AE;\n\tWed, 25 Feb 2026 14:19:12 +0100 (CET)","from us-smtp-delivery-124.mimecast.com\n\t(us-smtp-delivery-124.mimecast.com [170.10.129.124])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 0649861FA0\n\tfor ;\n\tWed, 25 Feb 2026 14:19:09 +0100 (CET)","from mail-wm1-f70.google.com (mail-wm1-f70.google.com\n\t[209.85.128.70]) by relay.mimecast.com with ESMTP with STARTTLS\n\t(version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id\n\tus-mta-657-MBHJWOBTPsen3z11XhxyZA-1; 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