From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from dggsgout11.his.huawei.com (dggsgout11.his.huawei.com [45.249.212.51]) (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 95D321AD5E5; Wed, 21 Aug 2024 13:37:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.51 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724247440; cv=none; b=gpinMigR3IruRqEU7dg7DF2hrm4wePvHz0c/rLlkgs9qMNSOl/WCXCrQ55V1ETqGpTwGDYXSlOaQhtZesX1BpklzgL61SJwqKa3CVv1gZX/8kOZwcfNGoqGKthFJE4yqS/1r6zaTg47jWKeoj/Rd6MaqzLdFydL2tIFl/F3Wc4s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724247440; c=relaxed/simple; bh=l6fAD1kJ5zU7U+OYaGUFn82eZe4l5R1fJ4+wNt3fzkc=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=ngoTEJesAUgqh1Hsvuzkyy13ENxqbpef0IdrWWwSGkcZpFnC3NujWHxgA9II+AeMbbxkLyrivaKi537FhVlDn1lsAmPlU/JoJANTS1JjhHol7dFl38mtlHhXz9twLzjv4yyouDoE3995E9+JVXaVCLe5An0AiDQt6DCH518+rts= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com; spf=none smtp.mailfrom=huaweicloud.com; arc=none smtp.client-ip=45.249.212.51 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=huaweicloud.com Received: from mail.maildlp.com (unknown [172.19.163.235]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTP id 4WpnSB05xQz4f3knx; Wed, 21 Aug 2024 21:36:58 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.128]) by mail.maildlp.com (Postfix) with ESMTP id A8D4B1A058E; Wed, 21 Aug 2024 21:37:07 +0800 (CST) Received: from huaweicloud.com (unknown [10.67.174.193]) by APP4 (Coremail) with SMTP id gCh0CgCHr4V97cVmXa5CCQ--.15501S5; Wed, 21 Aug 2024 21:37:07 +0800 (CST) From: Luo Gengkun To: peterz@infradead.org Cc: mingo@redhat.com, acme@kernel.org, namhyung@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, irogers@google.com, adrian.hunter@intel.com, kan.liang@linux.intel.com, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, luogengkun@huaweicloud.com Subject: [PATCH v4 1/2] perf/core: Fix small negative period being ignored Date: Wed, 21 Aug 2024 13:42:26 +0000 Message-Id: <20240821134227.577544-2-luogengkun@huaweicloud.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240821134227.577544-1-luogengkun@huaweicloud.com> References: <20240821134227.577544-1-luogengkun@huaweicloud.com> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CM-TRANSID:gCh0CgCHr4V97cVmXa5CCQ--.15501S5 X-Coremail-Antispam: 1UD129KBjvJXoWxXFyxtr48tr1DuF4DKw43Awb_yoW5uFyfpr WvyrnxKr4kGry5Kw1kAw1rXry5J3y8Aa17Wrn8KrW5Ca1Y9r4UJrWIvr12gr1kCF4Sva4I k3Z8Xr4fG3WvyF7anT9S1TB71UUUUjUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUHa14x267AKxVWrJVCq3wAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2048vs2IY020E87I2jVAFwI0_Jr4l82xGYIkIc2 x26xkF7I0E14v26r4j6ryUM28lY4IEw2IIxxk0rwA2F7IY1VAKz4vEj48ve4kI8wA2z4x0 Y4vE2Ix0cI8IcVAFwI0_Xr0_Ar1l84ACjcxK6xIIjxv20xvEc7CjxVAFwI0_Gr1j6F4UJw A2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x0267AKxVW0oVCq3wAa w2AFwI0_Jrv_JF1le2I262IYc4CY6c8Ij28IcVAaY2xG8wAqx4xG64xvF2IEw4CE5I8CrV C2j2WlYx0E2Ix0cI8IcVAFwI0_Jrv_JF1lYx0Ex4A2jsIE14v26r1j6r4UMcvjeVCFs4IE 7xkEbVWUJVW8JwACjcxG0xvY0x0EwIxGrwACjI8F5VA0II8E6IAqYI8I648v4I1lFIxGxc IEc7CjxVA2Y2ka0xkIwI1lc7CjxVAaw2AFwI0_Jw0_GFyl42xK82IYc2Ij64vIr41l4c8E cI0Ec7CjxVAaw2AFwI0_Jw0_GFyl4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxVAqx4xG67 AKxVWUJVWUGwC20s026x8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r1q6r43MIIY rxkI7VAKI48JMIIF0xvE2Ix0cI8IcVAFwI0_Gr0_Xr1lIxAIcVC0I7IYx2IY6xkF7I0E14 v26r4j6F4UMIIF0xvE42xK8VAvwI8IcIk0rVWUJVWUCwCI42IY6I8E87Iv67AKxVW8JVWx JwCI42IY6I8E87Iv6xkF7I0E14v26r4j6r4UJbIYCTnIWIevJa73UjIFyTuYvjfU1qXdUU UUU X-CM-SenderInfo: 5oxrwvpqjn3046kxt4xhlfz01xgou0bp/ In perf_adjust_period, we will first calculate period, and then use this period to calculate delta. However, when delta is less than 0, there will be a deviation compared to when delta is greater than or equal to 0. For example, when delta is in the range of [-14,-1], the range of delta = delta + 7 is between [-7,6], so the final value of delta/8 is 0. Therefore, the impact of -1 and -2 will be ignored. This is unacceptable when the target period is very short, because we will lose a lot of samples. Here are some tests and analyzes: before: # perf record -e cs -F 1000 ./a.out [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.022 MB perf.data (518 samples) ] # perf script ... a.out 396 257.956048: 23 cs: ffffffff81f4eeec schedul> a.out 396 257.957891: 23 cs: ffffffff81f4eeec schedul> a.out 396 257.959730: 23 cs: ffffffff81f4eeec schedul> a.out 396 257.961545: 23 cs: ffffffff81f4eeec schedul> a.out 396 257.963355: 23 cs: ffffffff81f4eeec schedul> a.out 396 257.965163: 23 cs: ffffffff81f4eeec schedul> a.out 396 257.966973: 23 cs: ffffffff81f4eeec schedul> a.out 396 257.968785: 23 cs: ffffffff81f4eeec schedul> a.out 396 257.970593: 23 cs: ffffffff81f4eeec schedul> ... after: # perf record -e cs -F 1000 ./a.out [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.058 MB perf.data (1466 samples) ] # perf script ... a.out 395 59.338813: 11 cs: ffffffff81f4eeec schedul> a.out 395 59.339707: 12 cs: ffffffff81f4eeec schedul> a.out 395 59.340682: 13 cs: ffffffff81f4eeec schedul> a.out 395 59.341751: 13 cs: ffffffff81f4eeec schedul> a.out 395 59.342799: 12 cs: ffffffff81f4eeec schedul> a.out 395 59.343765: 11 cs: ffffffff81f4eeec schedul> a.out 395 59.344651: 11 cs: ffffffff81f4eeec schedul> a.out 395 59.345539: 12 cs: ffffffff81f4eeec schedul> a.out 395 59.346502: 13 cs: ffffffff81f4eeec schedul> ... test.c int main() { for (int i = 0; i < 20000; i++) usleep(10); return 0; } # time ./a.out real 0m1.583s user 0m0.040s sys 0m0.298s The above results were tested on x86-64 qemu with KVM enabled using test.c as test program. Ideally, we should have around 1500 samples, but the previous algorithm had only about 500, whereas the modified algorithm now has about 1400. Further more, the new version shows 1 sample per 0.001s, while the previous one is 1 sample per 0.002s.This indicates that the new algorithm is more sensitive to small negative values compared to old algorithm. Fixes: bd2b5b12849a ("perf_counter: More aggressive frequency adjustment") Signed-off-by: Luo Gengkun Reviewed-by: Adrian Hunter --- kernel/events/core.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index c973e3c11e03..a9395bbfd4aa 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -4092,7 +4092,11 @@ static void perf_adjust_period(struct perf_event *event, u64 nsec, u64 count, bo period = perf_calculate_period(event, nsec, count); delta = (s64)(period - hwc->sample_period); - delta = (delta + 7) / 8; /* low pass filter */ + if (delta >= 0) + delta += 7; + else + delta -= 7; + delta /= 8; /* low pass filter */ sample_period = hwc->sample_period + delta; -- 2.34.1