From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1B82C190068; Tue, 10 Sep 2024 10:11:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725963119; cv=none; b=pqelc/7NvJgEm7hDdriBx9Kbeoxcamp7E7iLJP8EsGroXqqY33np5rGLEfVuSjNkKbKp0Eq2ksW1CQKc7+w1GDap/MyxPN/JuBMiPVI2o8ciSIi2M4NInQtV5hM9T6F3Grs/EaLM1Km54GvTjfB1h72E+kVC/pM8s69viahv8Rc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725963119; c=relaxed/simple; bh=FBOvexl4TaI4UyEM+y5/Z9V63jjH0+q/68MYLTS7RHA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=tsgiPp42T4NIDiwa99/BLIhX0g5CuJhSqsrrp2HjGdaMTSDEQOPbfHlN5BQP75gmixiFE+IY6fY2vMhq/i/osGmQ/c4TIEc4QTiCIRLk2PdT1EZIxWnkIQ9guxKOgBROr4I10xIMZIMg16G0EteyvzW2ENn61f+OZnUNRIreILw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=mGbHw45O; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="mGbHw45O" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 56233C4CEC3; Tue, 10 Sep 2024 10:11:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1725963118; bh=FBOvexl4TaI4UyEM+y5/Z9V63jjH0+q/68MYLTS7RHA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=mGbHw45O8ekjHtYCFcHMdNdAUxabJp+9DiluAP3tQBJpqCBrL2tNa20shrUT3ri+T CFmbb5X2VCg04DP8+m6Zocxou3zTG+GniiIgBQUJwKM8p2pOC0ztpugsq0Badx7sG5 BS6/t6SL5HoL/aFpg1KuCCsolYbt/RU2rBPdCOJo= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Yicong Yang , Barry Song , Christoph Hellwig , Sasha Levin Subject: [PATCH 6.1 105/192] dma-mapping: benchmark: Dont starve others when doing the test Date: Tue, 10 Sep 2024 11:32:09 +0200 Message-ID: <20240910092602.318737629@linuxfoundation.org> X-Mailer: git-send-email 2.46.0 In-Reply-To: <20240910092557.876094467@linuxfoundation.org> References: <20240910092557.876094467@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yicong Yang [ Upstream commit 54624acf8843375a6de3717ac18df3b5104c39c5 ] The test thread will start N benchmark kthreads and then schedule out until the test time finished and notify the benchmark kthreads to stop. The benchmark kthreads will keep running until notified to stop. There's a problem with current implementation when the benchmark kthreads number is equal to the CPUs on a non-preemptible kernel: since the scheduler will balance the kthreads across the CPUs and when the test time's out the test thread won't get a chance to be scheduled on any CPU then cannot notify the benchmark kthreads to stop. This can be easily reproduced on a VM (simulated with 16 CPUs) with PREEMPT_VOLUNTARY: estuary:/mnt$ ./dma_map_benchmark -t 16 -s 1 rcu: INFO: rcu_sched self-detected stall on CPU rcu: 10-...!: (5221 ticks this GP) idle=ed24/1/0x4000000000000000 softirq=142/142 fqs=0 rcu: (t=5254 jiffies g=-559 q=45 ncpus=16) rcu: rcu_sched kthread starved for 5255 jiffies! g-559 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=12 rcu: Unless rcu_sched kthread gets sufficient CPU time, OOM is now expected behavior. rcu: RCU grace-period kthread stack dump: task:rcu_sched state:R running task stack:0 pid:16 tgid:16 ppid:2 flags:0x00000008 Call trace __switch_to+0xec/0x138 __schedule+0x2f8/0x1080 schedule+0x30/0x130 schedule_timeout+0xa0/0x188 rcu_gp_fqs_loop+0x128/0x528 rcu_gp_kthread+0x1c8/0x208 kthread+0xec/0xf8 ret_from_fork+0x10/0x20 Sending NMI from CPU 10 to CPUs 0: NMI backtrace for cpu 0 CPU: 0 PID: 332 Comm: dma-map-benchma Not tainted 6.10.0-rc1-vanilla-LSE #8 Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015 pstate: 20400005 (nzCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : arm_smmu_cmdq_issue_cmdlist+0x218/0x730 lr : arm_smmu_cmdq_issue_cmdlist+0x488/0x730 sp : ffff80008748b630 x29: ffff80008748b630 x28: 0000000000000000 x27: ffff80008748b780 x26: 0000000000000000 x25: 000000000000bc70 x24: 000000000001bc70 x23: ffff0000c12af080 x22: 0000000000010000 x21: 000000000000ffff x20: ffff80008748b700 x19: ffff0000c12af0c0 x18: 0000000000010000 x17: 0000000000000001 x16: 0000000000000040 x15: ffffffffffffffff x14: 0001ffffffffffff x13: 000000000000ffff x12: 00000000000002f1 x11: 000000000001ffff x10: 0000000000000031 x9 : ffff800080b6b0b8 x8 : ffff0000c2a48000 x7 : 000000000001bc71 x6 : 0001800000000000 x5 : 00000000000002f1 x4 : 01ffffffffffffff x3 : 000000000009aaf1 x2 : 0000000000000018 x1 : 000000000000000f x0 : ffff0000c12af18c Call trace: arm_smmu_cmdq_issue_cmdlist+0x218/0x730 __arm_smmu_tlb_inv_range+0xe0/0x1a8 arm_smmu_iotlb_sync+0xc0/0x128 __iommu_dma_unmap+0x248/0x320 iommu_dma_unmap_page+0x5c/0xe8 dma_unmap_page_attrs+0x38/0x1d0 map_benchmark_thread+0x118/0x2c0 kthread+0xec/0xf8 ret_from_fork+0x10/0x20 Solve this by adding scheduling point in the kthread loop, so if there're other threads in the system they may have a chance to run, especially the thread to notify the test end. However this may degrade the test concurrency so it's recommended to run this on an idle system. Signed-off-by: Yicong Yang Acked-by: Barry Song Signed-off-by: Christoph Hellwig Signed-off-by: Sasha Levin --- kernel/dma/map_benchmark.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/kernel/dma/map_benchmark.c b/kernel/dma/map_benchmark.c index dafdc47ae5fc..3efdc5cfe390 100644 --- a/kernel/dma/map_benchmark.c +++ b/kernel/dma/map_benchmark.c @@ -89,6 +89,22 @@ static int map_benchmark_thread(void *data) atomic64_add(map_sq, &map->sum_sq_map); atomic64_add(unmap_sq, &map->sum_sq_unmap); atomic64_inc(&map->loops); + + /* + * We may test for a long time so periodically check whether + * we need to schedule to avoid starving the others. Otherwise + * we may hangup the kernel in a non-preemptible kernel when + * the test kthreads number >= CPU number, the test kthreads + * will run endless on every CPU since the thread resposible + * for notifying the kthread stop (in do_map_benchmark()) + * could not be scheduled. + * + * Note this may degrade the test concurrency since the test + * threads may need to share the CPU time with other load + * in the system. So it's recommended to run this benchmark + * on an idle system. + */ + cond_resched(); } out: -- 2.43.0