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 60877C433EF for ; Wed, 1 Jun 2022 06:45:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349896AbiFAGp3 (ORCPT ); Wed, 1 Jun 2022 02:45:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36692 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1347079AbiFAGp0 (ORCPT ); Wed, 1 Jun 2022 02:45:26 -0400 Received: from loongson.cn (mail.loongson.cn [114.242.206.163]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 3145195A3A for ; Tue, 31 May 2022 23:45:25 -0700 (PDT) Received: from [10.180.13.187] (unknown [10.180.13.187]) by mail.loongson.cn (Coremail) with SMTP id AQAAf9DxT0_yCpdiYT0LAA--.3609S3; Wed, 01 Jun 2022 14:45:06 +0800 (CST) Subject: Re: [PATCH v1] sched: there is no need to call switch_mm_irqs_off when sched between two user thread. To: Peter Zijlstra Cc: Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Valentin Schneider , linux-kernel@vger.kernel.org References: <1653998201-10230-1-git-send-email-wangming01@loongson.cn> From: Ming Wang Message-ID: Date: Wed, 1 Jun 2022 14:45:06 +0800 User-Agent: Mozilla/5.0 (X11; Linux loongarch64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-CM-TRANSID: AQAAf9DxT0_yCpdiYT0LAA--.3609S3 X-Coremail-Antispam: 1UD129KBjvJXoW7KryxJF4xAry7Kw45JrWUurg_yoW8Jw1kp3 yDJFy7GFnrua4jkay3Xwn5uryruws0gF47GFn0kFZ3JF98Kwn5Kr1rX3W3uFyIvr4fKrWa vr40v34IqFyUCaDanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUBmb7Iv0xC_tr1lb4IE77IF4wAFF20E14v26r4j6ryUM7CY07I2 0VC2zVCF04k26cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rw A2F7IY1VAKz4vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_Xr0_Ar1l84ACjcxK6xII jxv20xvEc7CjxVAFwI0_Cr0_Gr1UM28EF7xvwVC2z280aVAFwI0_Cr1j6rxdM28EF7xvwV C2z280aVCY1x0267AKxVW0oVCq3wAac4AC62xK8xCEY4vEwIxC4wAS0I0E0xvYzxvE52x0 82IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG6I80ewAv7VC0I7IYx2IY67AKxVWUGVWUXw Av7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFVCjc4AY6r1j6r4UM4x0Y48IcVAKI48JM4II rI8v6xkF7I0E8cxan2IY04v7Mxk0xIA0c2IEe2xFo4CEbIxvr21lc2xSY4AK6svPMxAIw2 8IcxkI7VAKI48JMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I0E5I8CrVAFwI0_Jr0_Jr4l x2IqxVCjr7xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWUtVW8ZwCIc40Y0x0EwIxGrw CI42IY6xIIjxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcVCY1x0267AKxVW8JVWxJwCI 42IY6xAIw20EY4v20xvaj40_WFyUJVCq3wCI42IY6I8E87Iv67AKxVWUJVW8JwCI42IY6I 8E87Iv6xkF7I0E14v26r4j6r4UJbIYCTnIWIevJa73UjIFyTuYvjxU7F1vUUUUU X-CM-SenderInfo: 5zdqwzxlqjiio6or00hjvr0hdfq/ Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/5/31 下午10:46, Peter Zijlstra wrote: > On Tue, May 31, 2022 at 07:56:41PM +0800, Ming Wang wrote: >> When condition (prev->active_mm == next->mm && !prev->mm) is met, >> the situation is as follows: >> >> user thread -> user thread >> >> There is not need switch_mm when sched between two user thread. >> Because they share the mm_struct. This can provide better >> performance when testing UnixBench. >> >> Signed-off-by: Ming Wang >> --- >> kernel/sched/core.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> index 696c649..9d7f6fb 100644 >> --- a/kernel/sched/core.c >> +++ b/kernel/sched/core.c >> @@ -5099,7 +5099,8 @@ asmlinkage __visible void schedule_tail(struct task_struct *prev) >> * case 'prev->active_mm == next->mm' through >> * finish_task_switch()'s mmdrop(). >> */ >> - switch_mm_irqs_off(prev->active_mm, next->mm, next); >> + if ((prev->active_mm != next->mm) || (!prev->mm)) >> + switch_mm_irqs_off(prev->active_mm, next->mm, next); > I think this needs to be inside switch_mm(). Architectures are free to > play silly games with what the current active mm is (and iirc x86 > actually does this). ok, thanks! And I will do it in architecture code.