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 7C784ECAAD2 for ; Mon, 29 Aug 2022 09:39:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229934AbiH2JjC (ORCPT ); Mon, 29 Aug 2022 05:39:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47156 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229620AbiH2JjB (ORCPT ); Mon, 29 Aug 2022 05:39:01 -0400 Received: from mail-yw1-x1133.google.com (mail-yw1-x1133.google.com [IPv6:2607:f8b0:4864:20::1133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9DBC65C9E6 for ; Mon, 29 Aug 2022 02:38:59 -0700 (PDT) Received: by mail-yw1-x1133.google.com with SMTP id 00721157ae682-33dba2693d0so180410687b3.12 for ; Mon, 29 Aug 2022 02:38:59 -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=GBvqua5cjMzjDQ/XgF9SZ1D4y+QsnVuyrt4amhV4btE=; b=dx6bRQ4JN/hF+3326YxFT0DmQuGRpE34IYiS96EVX69SRQeKSaYPwt5CrXJyN5/6Jy LU4sCb/nzEwY7rPM8KQoAIxIfvdbcNm2n40rDMqVfcTJScYRUNc6PFux701CkDOaVS3I p/4Hy2JiSHOOSzChWW0xl4APo4fnylJHJ9WrJKbGlSalEnDMAaddVjR/x9qZqTHorbQN oIVFtRs/0W/3z2F+EVui2fGdIizOdKUhrhCdwiHSyBf99GrsKuJ0tvJe2EHzoC0aQ+mz vJQY/hFbVFBQcwbB98qVRudkPkSpWvK3LFGhdzSkhwWir2jt11UNBByAnC4HQL4DbNqN Q4Wg== 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=GBvqua5cjMzjDQ/XgF9SZ1D4y+QsnVuyrt4amhV4btE=; b=i39nu7Zy8otjp6/PGXT8J/E1QIp7YrYI+rj6De8kSLTdJ/K8GiHl3mEBx3jxkiaZsA Rp1qZasRU1OQokd3fnHyZ0R+ZICHdDV/+A1Q3BhWWYR0EMSlVebc3ilbnxUIo1kfYwDZ WuNFbZvaWLfmd6ABgk3ib9GS7S3Qoit2DM9ImGjJBx4oDlMOtBLQKfrxhMiiuD51C+Rk rdUIA5tuDHxXrwYe416j8bgF+Ar5ZKAtQKve38GfTH+Anv/8iQ8OK4jmMENvOXHua7m3 rp3WUWjVkIjvF1qHBDk7Pb0Q3tBLpnQMQvAIduWonI7PNXaPk2STdd07x1Zn79R47Tkd qNzA== X-Gm-Message-State: ACgBeo33JhC8iP4yTIM8xChl4ht5LwXJCpviY47RqYEqYQLB9nUUo351 dlePr79VxpuHS9b9fx3iLFdSWhW0Wffpmk9d4JyO8w== X-Google-Smtp-Source: AA6agR6q7ad6sf4kgVlbFbNc5qY39/VlvvSlRemTzNOIPH7rueyubBC/OTF7pi8jTZlObaVAtjHrYIlq/M8iqBqxOiw= X-Received: by 2002:a81:4e04:0:b0:33d:c7dc:9e2b with SMTP id c4-20020a814e04000000b0033dc7dc9e2bmr8959772ywb.4.1661765938626; Mon, 29 Aug 2022 02:38:58 -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: Mon, 29 Aug 2022 11:38:22 +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 Mon, 29 Aug 2022 at 10:38, Peter Zijlstra wrote: > > On Wed, Aug 17, 2022 at 03:14:54PM +0200, Marco Elver wrote: > > 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? > > What context is this ran in? NMI should already have lockdep disabled. kgdb can enter via kgdb_nmicall*() but also via kgdb_handle_exception(), which isn't for NMI.