From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DB630C54E8B for ; Tue, 12 May 2020 11:22:07 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id B2382206DD for ; Tue, 12 May 2020 11:22:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="VskpU43Y" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B2382206DD Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=qLlfjCy3nV0S3wLhhinaUvIb8eD1/mCU0a4JPSEIF04=; b=VskpU43YXClJvg 1yOXEu5AXAlrf8j9V7CRRx8O3/ZfXBsjUP6nDFltVNyuVTJrsw3xL8ZpsAHHP4jqQmEzhg0GXIu78 wcYuxfT6THmS3S+XhGPL3T/svp1nyCaxJQoedvdRaPDGbBufkwMmvMosw4UkK4uws0ojDWtoAHPbJ pHQgD4FTB48TcUs8JfVkPvbBbHItf5WmlBKvoD7KUMXUPkqTDYYoSX8CvXgm3uLqLnpgh5vFb2ufk uCr4TF1S/YF+GOQTsLLS7e5+GVkB7FfzT7b2r+HkWFmU1DPd0Pq9Igg4LT5Ud/l2BWscVseeRg98z S+9/auQUGMnYnvLDQWDA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jYSz6-00054x-95; Tue, 12 May 2020 11:22:04 +0000 Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jYSz3-00054i-2F; Tue, 12 May 2020 11:22:01 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id DF124300261; Tue, 12 May 2020 13:21:58 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id AEE8620962E24; Tue, 12 May 2020 13:21:58 +0200 (CEST) Date: Tue, 12 May 2020 13:21:58 +0200 From: Peter Zijlstra To: Leo Yan Subject: Re: [PATCH v2 0/3] arm64: perf_event: Fix time offset prior to epoch Message-ID: <20200512112158.GD3001@hirez.programming.kicks-ass.net> References: <20200505135544.6003-1-leo.yan@linaro.org> <20200511092200.GF2957@hirez.programming.kicks-ass.net> <20200511092519.GA3001@hirez.programming.kicks-ass.net> <20200512063812.GA20352@leoy-ThinkPad-X240s> <20200512091918.GH2978@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200512091918.GH2978@hirez.programming.kicks-ass.net> X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Kate Stewart , Enrico Weigelt , Greg Kroah-Hartman , Alexander Shishkin , Marc Zyngier , Jiri Olsa , Daniel Lezcano , linux-kernel@vger.kernel.org, Arnaldo Carvalho de Melo , Paul Cercueil , Alexios Zavras , "Ahmed S. Darwish" , Ingo Molnar , linux-arm-kernel@lists.infradead.org, Catalin Marinas , Namhyung Kim , Thomas Gleixner , Will Deacon , "Ben Dooks \(Codethink\)" , Allison Randal Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, May 12, 2020 at 11:19:18AM +0200, Peter Zijlstra wrote: > Now, your arm64 counter is 56 bits, so wrapping is rare, but still, we > should probably fix that. And that probably needs an ABI extention > *sigh*. Something like so, on top of the other (2). --- --- a/arch/arm64/kernel/perf_event.c +++ b/arch/arm64/kernel/perf_event.c @@ -1174,6 +1174,7 @@ void arch_perf_update_userpage(struct pe userpg->cap_user_time = 0; userpg->cap_user_time_zero = 0; + userpg->cap_user_time_short = 0; do { rd = sched_clock_read_begin(&seq); @@ -1184,13 +1185,16 @@ void arch_perf_update_userpage(struct pe userpg->time_mult = rd->mult; userpg->time_shift = rd->shift; userpg->time_zero = rd->epoch_ns; + userpg->time_cycle = rd->epoch_cyc; + userpg->time_mask = rd->sched_clock_mask; /* * This isn't strictly correct, the ARM64 counter can be - * 'short' and then we get funnies when it wraps. The correct - * thing would be to extend the perf ABI with a cycle and mask - * value, but because wrapping on ARM64 is very rare in - * practise this 'works'. + * 'short' and then we get funnies when it wraps. But this + * 'works' with the cap_user_time ABI. + * + * When userspace knows about cap_user_time_short, it + * can do the correct thing. */ userpg->time_zero -= (rd->epoch_cyc * rd->mult) >> rd->shift; @@ -1215,4 +1219,5 @@ void arch_perf_update_userpage(struct pe */ userpg->cap_user_time = 1; userpg->cap_user_time_zero = 1; + userpg->cap_user_time_short = 1; } --- a/include/uapi/linux/perf_event.h +++ b/include/uapi/linux/perf_event.h @@ -532,9 +532,10 @@ struct perf_event_mmap_page { cap_bit0_is_deprecated : 1, /* Always 1, signals that bit 0 is zero */ cap_user_rdpmc : 1, /* The RDPMC instruction can be used to read counts */ - cap_user_time : 1, /* The time_* fields are used */ + cap_user_time : 1, /* The time_{shift,mult,offset} fields are used */ cap_user_time_zero : 1, /* The time_zero field is used */ - cap_____res : 59; + cap_user_time_short : 1, /* the time_{cycle,mask} fields are used */ + cap_____res : 58; }; }; @@ -593,13 +594,29 @@ struct perf_event_mmap_page { * ((rem * time_mult) >> time_shift); */ __u64 time_zero; + __u32 size; /* Header size up to __reserved[] fields. */ + __u32 __reserved_1; + + /* + * If cap_usr_time_short, the hardware clock is less than 64bit wide + * and we must compute the 'cyc' value, as used by cap_usr_time, as: + * + * cyc = time_cycles + ((cyc - time_cycles) & time_mask) + * + * NOTE: this form is explicitly chosen such that cap_usr_time_short + * is an extention on top of cap_usr_time, and code that doesn't + * know about cap_usr_time_short still works under the assumption + * the counter doesn't wrap. + */ + __u64 time_cycles; + __u64 time_mask; /* * Hole for extension of the self monitor capabilities */ - __u8 __reserved[118*8+4]; /* align to 1k. */ + __u8 __reserved[116*8]; /* align to 1k. */ /* * Control data for the mmap() data buffer. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel