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 5EC77C433EF for ; Thu, 9 Jun 2022 13:41:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343660AbiFINlq (ORCPT ); Thu, 9 Jun 2022 09:41:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38324 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343898AbiFINln (ORCPT ); Thu, 9 Jun 2022 09:41:43 -0400 Received: from mail-lj1-x22f.google.com (mail-lj1-x22f.google.com [IPv6:2a00:1450:4864:20::22f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 161812250A for ; Thu, 9 Jun 2022 06:41:40 -0700 (PDT) Received: by mail-lj1-x22f.google.com with SMTP id b7so13672844ljr.6 for ; Thu, 09 Jun 2022 06:41:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=PF28ZnQLVsGI2i7ul/dfgqup/8C1a0mc9TiBXmcosYU=; b=OAxGTJUe+XEVGmasomKjfTPF19BOrYj/fEHmMcR16tXmje2L2+5aMxRpp7TxlZz6+J yvlRV1lYkm0XlpTf4tltOaog/KE+I4t+0hk2WrYk3ACPv+Y7oF+vJN9L5yagoTRSCrS/ rworsIcSpHAopjkAjIDAp6gLDlsgNfeV+NvL3Db5jTsQRr/8ODDXA4w0x3waW2l6VyvY QuVdTcP44qHWxvGI92Tw8KlDERHWKynUAg3xzD4PoY+1SZM+nkIHAMReHJqIYi8fyhAZ GYTE2tO9RGEqmtMrpDG8JYNiKjyopdZujiWnnYuw9ckMZ1u0SBLz5YG8HyowXxR6qw40 Er/Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=PF28ZnQLVsGI2i7ul/dfgqup/8C1a0mc9TiBXmcosYU=; b=bRD9faZi0rpzbu/i15ElTdCQqx4WtI+mxZPTaXPIlF2nB5p6L/nnJFItkWi+YDwHCH CEZTinKi01zuoAWa23If/rE+S2+JgWNmA/YH4w8slfzFhzrGQVDKy8trF1G+mOFhbK5U UauaKoqehPGv51WXHBo5l4Cs456LKuskTxmTXhf7fir7DWsJ+M/9p+RlHRy5TMvHBdct +vLrXDSicT6MTOwT9UGvBJTbFecc5KKhaxdMfGxuEowBc3qfvph/hrdACCI25CDQp1lT 4znDDfG3Qc6DAiEtaUdbpyy5OxfPkVqy2z+Vc98d/OauMsTz9xeW4LbPWfLtOHwHCJfm 196Q== X-Gm-Message-State: AOAM533qLdIolBV0ejquvhzcoO2GaDXntj8FolFO4JeJqLgi4vzr2nzn 4ttPHPlV00gvPeo+18ZN7jIA5CSIXr/6hDmkoz5EPA== X-Google-Smtp-Source: ABdhPJxKwbLXuKSnIJ3Phiqmieh/Wr9lduzAjt/Ld23SCuasFCRov3KdDNmTk8meN2KOewMYkB2L7tKO5zGU0Tha5P4= X-Received: by 2002:a2e:b0fc:0:b0:255:6f92:f9d4 with SMTP id h28-20020a2eb0fc000000b002556f92f9d4mr22136645ljl.92.1654782098160; Thu, 09 Jun 2022 06:41:38 -0700 (PDT) MIME-Version: 1.0 References: <20220609113046.780504-1-elver@google.com> <20220609113046.780504-6-elver@google.com> In-Reply-To: From: Dmitry Vyukov Date: Thu, 9 Jun 2022 15:41:26 +0200 Message-ID: Subject: Re: [PATCH 5/8] perf/hw_breakpoint: Remove useless code related to flexible breakpoints To: Marco Elver Cc: Peter Zijlstra , Frederic Weisbecker , Ingo Molnar , Thomas Gleixner , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , 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 Thu, 9 Jun 2022 at 14:04, Dmitry Vyukov wrote: > > On Thu, 9 Jun 2022 at 13:31, Marco Elver wrote: > > > > Flexible breakpoints have never been implemented, with > > bp_cpuinfo::flexible always being 0. Unfortunately, they still occupy 4 > > bytes in each bp_cpuinfo and bp_busy_slots, as well as computing the max > > flexible count in fetch_bp_busy_slots(). > > > > This again causes suboptimal code generation, when we always know that > > `!!slots.flexible` will be 0. > > > > Just get rid of the flexible "placeholder" and remove all real code > > related to it. Make a note in the comment related to the constraints > > algorithm but don't remove them from the algorithm, so that if in future > > flexible breakpoints need supporting, it should be trivial to revive > > them (along with reverting this change). > > > > Signed-off-by: Marco Elver > > Was added in 2009. > > Acked-by: Dmitry Vyukov > > > --- > > kernel/events/hw_breakpoint.c | 12 +++--------- > > 1 file changed, 3 insertions(+), 9 deletions(-) > > > > diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c > > index 5f40c8dfa042..afe0a6007e96 100644 > > --- a/kernel/events/hw_breakpoint.c > > +++ b/kernel/events/hw_breakpoint.c > > @@ -46,8 +46,6 @@ struct bp_cpuinfo { > > #else > > unsigned int *tsk_pinned; > > #endif > > - /* Number of non-pinned cpu/task breakpoints in a cpu */ > > - unsigned int flexible; /* XXX: placeholder, see fetch_this_slot() */ > > }; > > > > static DEFINE_PER_CPU(struct bp_cpuinfo, bp_cpuinfo[TYPE_MAX]); > > @@ -71,7 +69,6 @@ static bool constraints_initialized __ro_after_init; > > /* Gather the number of total pinned and un-pinned bp in a cpuset */ > > struct bp_busy_slots { Do we also want to remove this struct altogether? Now it becomes just an int counter. > > unsigned int pinned; > > - unsigned int flexible; > > }; > > > > /* Serialize accesses to the above constraints */ > > @@ -213,10 +210,6 @@ fetch_bp_busy_slots(struct bp_busy_slots *slots, struct perf_event *bp, > > > > if (nr > slots->pinned) > > slots->pinned = nr; > > - > > - nr = info->flexible; > > - if (nr > slots->flexible) > > - slots->flexible = nr; > > } > > } > > > > @@ -299,7 +292,8 @@ __weak void arch_unregister_hw_breakpoint(struct perf_event *bp) > > } > > > > /* > > - * Constraints to check before allowing this new breakpoint counter: > > + * Constraints to check before allowing this new breakpoint counter. Note that > > + * flexible breakpoints are currently unsupported -- see fetch_this_slot(). > > * > > * == Non-pinned counter == (Considered as pinned for now) > > * > > @@ -366,7 +360,7 @@ static int __reserve_bp_slot(struct perf_event *bp, u64 bp_type) > > fetch_this_slot(&slots, weight); > > > > /* Flexible counters need to keep at least one slot */ > > - if (slots.pinned + (!!slots.flexible) > hw_breakpoint_slots_cached(type)) > > + if (slots.pinned > hw_breakpoint_slots_cached(type)) > > return -ENOSPC; > > > > ret = arch_reserve_bp_slot(bp); > > -- > > 2.36.1.255.ge46751e96f-goog > >