From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f41.google.com (mail-pa0-f41.google.com [209.85.220.41]) by kanga.kvack.org (Postfix) with ESMTP id 453B76B0255 for ; Thu, 3 Dec 2015 13:36:21 -0500 (EST) Received: by pacdm15 with SMTP id dm15so72984130pac.3 for ; Thu, 03 Dec 2015 10:36:21 -0800 (PST) Received: from mail-pf0-x22d.google.com (mail-pf0-x22d.google.com. [2607:f8b0:400e:c00::22d]) by mx.google.com with ESMTPS id n88si13455030pfb.56.2015.12.03.10.36.20 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 03 Dec 2015 10:36:20 -0800 (PST) Received: by pfu207 with SMTP id 207so12392381pfu.2 for ; Thu, 03 Dec 2015 10:36:20 -0800 (PST) Message-ID: <56608BA2.2050300@linaro.org> Date: Thu, 03 Dec 2015 10:36:18 -0800 From: "Shi, Yang" MIME-Version: 1.0 Subject: Re: [PATCH V2 2/7] mm/gup: add gup trace points References: <1449096813-22436-1-git-send-email-yang.shi@linaro.org> <1449096813-22436-3-git-send-email-yang.shi@linaro.org> <565F8092.7000001@intel.com> <20151202231348.7058d6e2@grimm.local.home> In-Reply-To: <20151202231348.7058d6e2@grimm.local.home> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Steven Rostedt , Dave Hansen Cc: akpm@linux-foundation.org, mingo@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linaro-kernel@lists.linaro.org On 12/2/2015 8:13 PM, Steven Rostedt wrote: > On Wed, 2 Dec 2015 15:36:50 -0800 > Dave Hansen wrote: > >> On 12/02/2015 02:53 PM, Yang Shi wrote: >>> diff --git a/mm/gup.c b/mm/gup.c >>> index deafa2c..10245a4 100644 >>> --- a/mm/gup.c >>> +++ b/mm/gup.c >>> @@ -13,6 +13,9 @@ >>> #include >>> #include >>> >>> +#define CREATE_TRACE_POINTS >>> +#include >>> + >>> #include >>> #include >> >> This needs to be _the_ last thing that gets #included. Otherwise, you >> risk colliding with any other trace header that gets implicitly included >> below. > > Agreed. > >> >>> @@ -1340,6 +1346,8 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write, >>> start, len))) >>> return 0; >>> >>> + trace_gup_get_user_pages_fast(start, nr_pages, write, pages); >>> + >>> /* >>> * Disable interrupts. We use the nested form as we can already have >>> * interrupts disabled by get_futex_key. >> >> It would be _really_ nice to be able to see return values from the >> various gup calls as well. Is that feasible? > > Only if you rewrite the functions to have a single return code path > that we can add a tracepoint too. Or have a wrapper function that gets Yes. My preliminary test just could cover the success case. gup could return errno from different a few code path. > called directly that calls these functions internally and the tracepoint > can trap the return value. This will incur more changes in other subsystems (futex, kvm, etc), I'm not sure if it is worth making such changes to get return value. > I can probably make function_graph tracer give return values, although > it will give a return value for void functions as well. And it may give > long long returns for int returns that may have bogus data in the > higher bits. If the return value requirement is not limited to gup, the approach sounds more reasonable. Thanks, Yang > > -- Steve > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org