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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 31EF6C28B2B for ; Wed, 17 Aug 2022 13:16:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239915AbiHQNQU (ORCPT ); Wed, 17 Aug 2022 09:16:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46250 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239220AbiHQNP5 (ORCPT ); Wed, 17 Aug 2022 09:15:57 -0400 Received: from mail-yw1-x1135.google.com (mail-yw1-x1135.google.com [IPv6:2607:f8b0:4864:20::1135]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AFF028C016 for ; Wed, 17 Aug 2022 06:15:31 -0700 (PDT) Received: by mail-yw1-x1135.google.com with SMTP id 00721157ae682-3321c2a8d4cso176942207b3.5 for ; Wed, 17 Aug 2022 06:15:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc; bh=4x9/R2mHqDBSBsINZoYzu53n4+/x9xPXewr5G0XEr34=; b=Ta7vQAWfgNwLeo8X+pcdJ6JyCnUcaqj1Ews44KLWjJGhgXZv20jGydY8asVvhmMfNz b5Fzq6C/S2NXkgfMPJzpJcfXtNp/XsSJDaSorCNhL1D/nzqkMFU7Du+YXm0LpKulY9IK /76nM6mT8xUUP8UaTC1eN5M2TkbrsohpqC0/E8YxXYpbdWBeaceJ/x8g5odhImXtyrc1 qOyIpz90N1Ejyl+l9w55WOS+8npqTm4TRnzX3bA4a2avvsii63eJWYfy6fWyxSZaHQWM Qo0/XLJ6ZGGdQy6n6h+9ZeH4bseaOSQZpSngSXr1oW9GbmtitbnwZya8r8OT9qqDsOW5 Pddg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc; bh=4x9/R2mHqDBSBsINZoYzu53n4+/x9xPXewr5G0XEr34=; b=i5x/1hd5FNzTxqkpSQWnOUlY5CBCQGlQQ4snR90VB9dUay298IWy2+PxVIuoMAiKOf 4VYeBpcc4oX2DE72T0tEAFyftfVxfIdP/pe9THBOmaUbpaeinoaIhHxJ9ND5Ow7SEVNt OlI4lly9///gJIDgn9Px9lJmskZDxTCLAaRHya3M+QLPGnoewUhWtWgHW2haUKaLjdg+ wMx9ckzHL1Ysa/Zz8aoMIyVGmu+5amz/w8Yfv9QRykZlYjeMxguhhJHu+vdsMxJEyqms Ypmq9xLnXK7ITHtQjPf8g0jAvBw5RC1yySAiJ7AcKVkoUxJvtYOeNX5pJ0ZhP40SM+us PBVg== X-Gm-Message-State: ACgBeo2rZQFwH0ztqmifQ6kT9THkIZWysUnXRNiGFl6U/aZHp76Ri543 uNUt6cpwuo0muOWK20kkSTNPGKlILJNhDFI5Ex5Cmg== X-Google-Smtp-Source: AA6agR4J3cyIT0SWBYaiCeztXduj+LhF+ocuDdNtn7hGLnqyHtxrllFHNLPRhY47QfH++sCFFlwAFNLyvGB5+UaJKNI= X-Received: by 2002:a5b:c8b:0:b0:688:ebe9:3d05 with SMTP id i11-20020a5b0c8b000000b00688ebe93d05mr12303544ybq.553.1660742130329; Wed, 17 Aug 2022 06:15:30 -0700 (PDT) MIME-Version: 1.0 References: <20220704150514.48816-1-elver@google.com> <20220704150514.48816-12-elver@google.com> In-Reply-To: From: Marco Elver Date: Wed, 17 Aug 2022 15:14:54 +0200 Message-ID: Subject: Re: [PATCH v3 11/14] perf/hw_breakpoint: Reduce contention with large number of tasks To: Peter Zijlstra Cc: Frederic Weisbecker , Ingo Molnar , Thomas Gleixner , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Dmitry Vyukov , Michael Ellerman , linuxppc-dev@lists.ozlabs.org, linux-perf-users@vger.kernel.org, x86@kernel.org, linux-sh@vger.kernel.org, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org On Wed, 17 Aug 2022 at 15:03, Peter Zijlstra wrote: > > On Mon, Jul 04, 2022 at 05:05:11PM +0200, Marco Elver wrote: > > +static bool bp_constraints_is_locked(struct perf_event *bp) > > +{ > > + struct mutex *tsk_mtx = get_task_bps_mutex(bp); > > + > > + return percpu_is_write_locked(&bp_cpuinfo_sem) || > > + (tsk_mtx ? mutex_is_locked(tsk_mtx) : > > + percpu_is_read_locked(&bp_cpuinfo_sem)); > > +} > > > @@ -426,18 +521,28 @@ static int modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type) > > */ > > int dbg_reserve_bp_slot(struct perf_event *bp) > > { > > - if (mutex_is_locked(&nr_bp_mutex)) > > + int ret; > > + > > + if (bp_constraints_is_locked(bp)) > > return -1; > > > > - return __reserve_bp_slot(bp, bp->attr.bp_type); > > + /* Locks aren't held; disable lockdep assert checking. */ > > + lockdep_off(); > > + ret = __reserve_bp_slot(bp, bp->attr.bp_type); > > + lockdep_on(); > > + > > + return ret; > > } > > > > int dbg_release_bp_slot(struct perf_event *bp) > > { > > - if (mutex_is_locked(&nr_bp_mutex)) > > + if (bp_constraints_is_locked(bp)) > > return -1; > > > > + /* Locks aren't held; disable lockdep assert checking. */ > > + lockdep_off(); > > __release_bp_slot(bp, bp->attr.bp_type); > > + lockdep_on(); > > > > return 0; > > } > > Urggghhhh... this is horrible crap. That is, the current code is that > and this makes it worse :/ Heh, yes and when I looked at it I really wanted to see if it can change. But from what I can tell, when the kernel debugger is being attached, the kernel does stop everything it does and we need the horrible thing above to not deadlock. And these dbg_ functions are not normally used, so I decided to leave it as-is. Suggestions?