From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7B6A2D507 for ; Mon, 15 May 2023 17:58:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 98645C4339B; Mon, 15 May 2023 17:58:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1684173482; bh=t3HksqggWWqKlzkJo9evKIUOtv6TPlQa/XMBnvOdHs8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=W8xMhLaLmJOT7eQssZpCPXSz8VmIIdo7yEw7gJ6oTUj1sly2LZqk3WvUD12qDFpUG Y5iN8H/TDk/L0Y+XwkXyRUvEXFq60uRajLAKaMHNXD2zPoxyEf/mDoNuq2xDNyBUhV NIenhK2WHKgy3dAQ2UrUroar/tX/LBoJYWL+ZkYk= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Yunfeng Ye , Thomas Gleixner , Sasha Levin Subject: [PATCH 5.4 070/282] tick/sched: Reduce seqcount held scope in tick_do_update_jiffies64() Date: Mon, 15 May 2023 18:27:28 +0200 Message-Id: <20230515161724.332012350@linuxfoundation.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20230515161722.146344674@linuxfoundation.org> References: <20230515161722.146344674@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Yunfeng Ye [ Upstream commit 94ad2e3cedb82af034f6d97c58022f162b669f9b ] If jiffies are up to date already (caller lost the race against another CPU) there is no point to change the sequence count. Doing that just forces other CPUs into the seqcount retry loop in tick_nohz_next_event() for nothing. Just bail out early. [ tglx: Rewrote most of it ] Signed-off-by: Yunfeng Ye Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20201117132006.462195901@linutronix.de Stable-dep-of: e9523a0d8189 ("tick/common: Align tick period with the HZ tick.") Signed-off-by: Sasha Levin --- kernel/time/tick-sched.c | 47 +++++++++++++++++++--------------------- 1 file changed, 22 insertions(+), 25 deletions(-) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 1dfa53494164a..eaeeb4bb1f8ab 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -84,38 +84,35 @@ static void tick_do_update_jiffies64(ktime_t now) /* Reevaluate with jiffies_lock held */ raw_spin_lock(&jiffies_lock); + if (ktime_before(now, tick_next_period)) { + raw_spin_unlock(&jiffies_lock); + return; + } + write_seqcount_begin(&jiffies_seq); - delta = ktime_sub(now, last_jiffies_update); - if (delta >= tick_period) { + last_jiffies_update = ktime_add(last_jiffies_update, tick_period); - delta = ktime_sub(delta, tick_period); - last_jiffies_update = ktime_add(last_jiffies_update, - tick_period); + delta = ktime_sub(now, tick_next_period); + if (unlikely(delta >= tick_period)) { + /* Slow path for long idle sleep times */ + s64 incr = ktime_to_ns(tick_period); - /* Slow path for long timeouts */ - if (unlikely(delta >= tick_period)) { - s64 incr = ktime_to_ns(tick_period); + ticks = ktime_divns(delta, incr); - ticks = ktime_divns(delta, incr); + last_jiffies_update = ktime_add_ns(last_jiffies_update, + incr * ticks); + } - last_jiffies_update = ktime_add_ns(last_jiffies_update, - incr * ticks); - } - do_timer(++ticks); + do_timer(++ticks); + + /* + * Keep the tick_next_period variable up to date. WRITE_ONCE() + * pairs with the READ_ONCE() in the lockless quick check above. + */ + WRITE_ONCE(tick_next_period, + ktime_add(last_jiffies_update, tick_period)); - /* - * Keep the tick_next_period variable up to date. - * WRITE_ONCE() pairs with the READ_ONCE() in the lockless - * quick check above. - */ - WRITE_ONCE(tick_next_period, - ktime_add(last_jiffies_update, tick_period)); - } else { - write_seqcount_end(&jiffies_seq); - raw_spin_unlock(&jiffies_lock); - return; - } write_seqcount_end(&jiffies_seq); raw_spin_unlock(&jiffies_lock); update_wall_time(); -- 2.39.2