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Received: from szxga06-in.huawei.com ([45.249.212.32]) by bombadil.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1lje5v-00G4Nz-JF for linux-arm-kernel@lists.infradead.org; Thu, 20 May 2021 08:31:53 +0000 Received: from dggems706-chm.china.huawei.com (unknown [172.30.72.60]) by szxga06-in.huawei.com (SkyGuard) with ESMTP id 4Fm2w331W8zmX7y; Thu, 20 May 2021 16:29:23 +0800 (CST) Received: from dggpemm000003.china.huawei.com (7.185.36.128) by dggems706-chm.china.huawei.com (10.3.19.183) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Thu, 20 May 2021 16:31:39 +0800 Received: from [10.67.102.248] (10.67.102.248) by dggpemm000003.china.huawei.com (7.185.36.128) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Thu, 20 May 2021 16:31:39 +0800 Subject: Re: [PATCH] arm_pmu: Fix write counter incorrect in ARMv7 big-endian mode To: Mark Rutland , CC: , , , , , , , , , , References: <20210430012659.232110-1-yangjihong1@huawei.com> <20210430123408.GD53304@C02TD0UTHF1T.local> From: Yang Jihong Message-ID: Date: Thu, 20 May 2021 16:31:31 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <20210430123408.GD53304@C02TD0UTHF1T.local> Content-Language: en-US X-Originating-IP: [10.67.102.248] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To dggpemm000003.china.huawei.com (7.185.36.128) X-CFilter-Loop: Reflected X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210520_013151_987354_2E9BB852 X-CRM114-Status: GOOD ( 20.56 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hello, Mark On 2021/4/30 20:34, Mark Rutland wrote: > On Fri, Apr 30, 2021 at 09:26:59AM +0800, Yang Jihong wrote: >> Commit 3a95200d3f89a ("arm_pmu: Change API to support 64bit counter values") >> changes the input "value" type from 32-bit to 64-bit, >> which introduces the following problem: >> ARMv7 PMU counters is 32-bit width, in big-endian mode, write counter uses >> high 32-bit, which writes an incorrect value. > > It might be worth noting that the reason for this is that when a 64-bit > value is split across two 32-bit registers, the high/low halves are > split to match how LDRD would load a 64-bit quantity (and so differs > across big/little endian), but the "r" constraint consistently uses the > first of the two regiseters. > > Given that, this patch makes sense to me (and I didn't spot any related > issues), so: > > Acked-by: Mark Rutland Thank you for your review. :) Yang. > > Will, I assume you'll pick this up. > > Mark. > >> >> Before: >> >> Performance counter stats for 'ls': >> >> 2.22 msec task-clock # 0.675 CPUs utilized >> 0 context-switches # 0.000 K/sec >> 0 cpu-migrations # 0.000 K/sec >> 49 page-faults # 0.022 M/sec >> 2150476593 cycles # 966.663 GHz >> 2148588788 instructions # 1.00 insn per cycle >> 2147745484 branches # 965435.074 M/sec >> 2147508540 branch-misses # 99.99% of all branches >> >> None of the above hw event counters are correct. >> >> Solution: >> >> "value" forcibly converted to 32-bit type before being written to PMU register. >> >> After: >> >> Performance counter stats for 'ls': >> >> 2.09 msec task-clock # 0.681 CPUs utilized >> 0 context-switches # 0.000 K/sec >> 0 cpu-migrations # 0.000 K/sec >> 46 page-faults # 0.022 M/sec >> 2807301 cycles # 1.344 GHz >> 1060159 instructions # 0.38 insn per cycle >> 250496 branches # 119.914 M/sec >> 23192 branch-misses # 9.26% of all branches >> >> Fixes: 3a95200d3f89a ("arm_pmu: Change API to support 64bit counter values") >> Signed-off-by: Yang Jihong >> --- >> arch/arm/kernel/perf_event_v7.c | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/arch/arm/kernel/perf_event_v7.c b/arch/arm/kernel/perf_event_v7.c >> index 2924d7910b10..eb2190477da1 100644 >> --- a/arch/arm/kernel/perf_event_v7.c >> +++ b/arch/arm/kernel/perf_event_v7.c >> @@ -773,10 +773,10 @@ static inline void armv7pmu_write_counter(struct perf_event *event, u64 value) >> pr_err("CPU%u writing wrong counter %d\n", >> smp_processor_id(), idx); >> } else if (idx == ARMV7_IDX_CYCLE_COUNTER) { >> - asm volatile("mcr p15, 0, %0, c9, c13, 0" : : "r" (value)); >> + asm volatile("mcr p15, 0, %0, c9, c13, 0" : : "r" ((u32)value)); >> } else { >> armv7_pmnc_select_counter(idx); >> - asm volatile("mcr p15, 0, %0, c9, c13, 2" : : "r" (value)); >> + asm volatile("mcr p15, 0, %0, c9, c13, 2" : : "r" ((u32)value)); >> } >> } >> >> -- >> 2.30.GIT >> > . > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel