From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751581AbdKUIah (ORCPT ); Tue, 21 Nov 2017 03:30:37 -0500 Received: from szxga06-in.huawei.com ([45.249.212.32]:34805 "EHLO huawei.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1751554AbdKUIaf (ORCPT ); Tue, 21 Nov 2017 03:30:35 -0500 Subject: Re: [PATCH] perf parse events: Fix invalid precise_ip handling To: Jiri Olsa CC: , , , , , , References: <1510302517-33383-1-git-send-email-zhangmengting@huawei.com> <20171110103900.GA10233@krava> <6dc43edb-0c33-6d82-71a3-3d7cac10a881@huawei.com> <20171120073341.GA5497@krava> From: zhangmengting Message-ID: <1a249a21-5e93-7434-8b6f-08241513dceb@huawei.com> Date: Tue, 21 Nov 2017 16:30:09 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0 MIME-Version: 1.0 In-Reply-To: <20171120073341.GA5497@krava> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Originating-IP: [10.177.28.139] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2017/11/20 15:33, Jiri Olsa wrote: > On Wed, Nov 15, 2017 at 09:00:03AM +0800, zhangmengting wrote: >> Hi Jiri, thanks for your detailed review, please see my comments inline. >> >> >> On 2017/11/10 18:39, Jiri Olsa wrote: >>> On Fri, Nov 10, 2017 at 04:28:37PM +0800, Mengting Zhang wrote: >>> >>> SNIP >>> >>>> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c >>>> index 39b1596..25225f4 100644 >>>> --- a/tools/perf/util/parse-events.c >>>> +++ b/tools/perf/util/parse-events.c >>>> @@ -1369,6 +1369,32 @@ struct event_modifier { >>>> int pinned; >>>> }; >>>> +static int perf_get_max_precise_ip(void) >>>> +{ >>>> + int max_precise_ip = 0; >>>> + struct perf_event_attr attr = { >>>> + .type = PERF_TYPE_HARDWARE, >>>> + .config = PERF_COUNT_HW_CPU_CYCLES, >>>> + }; >>>> + >>>> + event_attr_init(&attr); >>>> + >>>> + attr.precise_ip = 3; >>>> + attr.sample_period = 1; >>>> + >>>> + while (attr.precise_ip != 0) { >>>> + int fd = sys_perf_event_open(&attr, 0, -1, -1, 0); >>>> + if (fd != -1){ >>>> + close(fd); >>>> + break; >>>> + } >>>> + --attr.precise_ip; >>>> + } >>>> + max_precise_ip = attr.precise_ip; >>>> + >>>> + return max_precise_ip; >>>> +} >>> we already have a function for that, please check perf_event_attr__set_max_precise_ip >> Yeah, I've checked that function. But perf_event_attr__set_max_precise_ip() >> will change attr.precise_ip >> into the max precise ip available. >> >> In this case, perf should only check whether the user-specified precise_ip >> is greater than the max >> precise_ip without changing it into maximum. Here, introduce >> perf_get_max_precise_ip() to return >> the max precise ip and do not change attr.precise_ip. >> >> But you reminds me that perf_get_max_precise_ip() can be simplied. > well both do the same.. probe kernel for max precise level, > so we can keep just one function for that OKay, I will just keep that function for probing max precise level. >>> also I think the precise level is not generic for all the events, >>> so you should check it for specific perf_event_attr later, when >>> the attr is ready, not in modifier parsing >> You are right, and I would check it for specific perf_event_attr. >> >> BTW, I have a question. If the user-specified precise_ip is greater than the >> max precise_ip, I wonder >> whether it is better to adjust the user-specified precise_ip to the maximum >> available. > no, I think that user defined precise level should stay the > way the user wants it.. we don't want more angry users ;-) Humm, I am sorry for being unclear. If the user defined precise level is greater than the max precise level, I think there are two ways to deal with it. 1. return EINVAL to indicate the invalid precise_ip setting; 2. adjust to the max precise level available and give message to indicate the adjustment. Since we should check user-defined precise level in perf_evsel__config(), when the attr is ready, I think there is a problem with method 1, if we keep the user defined precise level stay the way the user wants it. With method 1, we have to let perf_evsel__config() return value and show errno. And this change will affect many related functions, such as perf_evlist__config(), and files. With method 2, we don't need to change the return type of perf_evsel__config(). Am I right? > > jirka > > . >