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Fri, 28 Aug 2020 01:33:42 -0700 (PDT) Date: Fri, 28 Aug 2020 10:33:25 +0200 From: Jean-Philippe Brucker To: "Song Bao Hua (Barry Song)" Subject: Re: [PATCH] iommu/arm-smmu-v3: add tracepoints for cmdq_issue_cmdlist Message-ID: <20200828083325.GC3825485@myrica> References: <20200827093351.15244-1-song.bao.hua@hisilicon.com> <20200828074107.GB3825485@myrica> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: Cc: "will@kernel.org" , "iommu@lists.linux-foundation.org" , "robin.murphy@arm.com" , Linuxarm , "linux-arm-kernel@lists.infradead.org" X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Fri, Aug 28, 2020 at 07:55:18AM +0000, Song Bao Hua (Barry Song) wrote: > > > > -----Original Message----- > > From: Jean-Philippe Brucker [mailto:jean-philippe@linaro.org] > > Sent: Friday, August 28, 2020 7:41 PM > > To: Song Bao Hua (Barry Song) > > Cc: iommu@lists.linux-foundation.org; linux-arm-kernel@lists.infradead.org; > > robin.murphy@arm.com; will@kernel.org; Linuxarm > > Subject: Re: [PATCH] iommu/arm-smmu-v3: add tracepoints for > > cmdq_issue_cmdlist > > > > Hi, > > > > On Thu, Aug 27, 2020 at 09:33:51PM +1200, Barry Song wrote: > > > cmdq_issue_cmdlist() is the hotspot that uses a lot of time. This > > > patch adds tracepoints for it to help debug. > > > > > > Signed-off-by: Barry Song > > > --- > > > * can furthermore develop an eBPF program to benchmark using this > > > trace > > > > Have you tried using kprobe and kretprobe instead of tracepoints? > > Any noticeable performance drop? > > Yes. Pls read this email. > kprobe overhead and OPTPROBES implementation on ARM64 > https://www.spinics.net/lists/arm-kernel/msg828788.html Thanks for the pointer. I'm asking because I've been working on BPF trampolines (fentry/fexit) for arm64, which reduce the overhead of BPF tracing, and am looking for confirmation that it's needed before spending more time on it. Perhaps OPTPROBE would be a better first step, though, it seems more generic. Thanks, Jean _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu