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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D0613C433FE for ; Wed, 20 Oct 2021 10:37:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AFE0C60EE9 for ; Wed, 20 Oct 2021 10:37:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230091AbhJTKjx (ORCPT ); Wed, 20 Oct 2021 06:39:53 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:54275 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229864AbhJTKjw (ORCPT ); Wed, 20 Oct 2021 06:39:52 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1634726258; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=4yrUw21h+zQ2wXbMw73pU6qHpDvhPbFCoQi4iYgtHLM=; b=anKef6g46t2Vl5EU6d+mR8ma3AZQHiWAGAfvmpT13bE0dRDkByleNSMlWeve7OTDS/Kh4g /akgzy7dbefDEwJLiq2vxLBPW5uStymFnIN+/g8A1OdECxrNwB8dT4DVPStuo7PSVjXMtx 264f8WixVRbVCLcBAJDQGYz0CpVzWtc= Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-204-bMAMkTsHN3CNVwUKl3-rug-1; Wed, 20 Oct 2021 06:37:36 -0400 X-MC-Unique: bMAMkTsHN3CNVwUKl3-rug-1 Received: by mail-ed1-f70.google.com with SMTP id v9-20020a50d849000000b003dcb31eabaaso2871140edj.13 for ; Wed, 20 Oct 2021 03:37:36 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=4yrUw21h+zQ2wXbMw73pU6qHpDvhPbFCoQi4iYgtHLM=; b=5FuLujhG40GWluvQIFBV11pUPuJ8FXqGZAhDr2NRg1wwytkxh7zfLtLL2sOs0IxcNk RJN4rM2ddsF3KVN0TdId6kRQwSwX49KiwXuf/ykH/yGz2TRcwHdu5UOh1F5RH4J/zay5 bB/Fc0e21nkQj2+nJlx+VBBSatkvng3DHfEAzsaNBYLFtbSolBydvoTbmaeN4FoC1KZD pWv2KbHu4ILlJF674kWo/I6kBGAwsjSDqoxZIwlAV7Q8KRsQbZ0Ga8j7ac1cRVK3ijrQ p1e2fntxq5QyIjiZoB/IFCevgGrFRJjbjMp3fY6Wo1WxzY9SSOb2kMfxJ086gyN1UZEA 2rpw== X-Gm-Message-State: AOAM530kiJhPeNWhiD5R2eh52L8QkKh1SDDQh/3oId8d4TNSzCWGwIzO ilZ9rjHBXwKbLlUkP233kiUbLnTYwjHMb3bKtyZgbugs+8H2TS6+/+bhME2HLsoGZT2YMtysgtD xzbuTgIckcysgxXmaMHOxE3SZ X-Received: by 2002:a17:907:7fa8:: with SMTP id qk40mr43860947ejc.445.1634726255672; Wed, 20 Oct 2021 03:37:35 -0700 (PDT) X-Google-Smtp-Source: ABdhPJyMWzsiJlUJ6VMXTDtVVr8gloUIzhLnBOqnnnGEXhwBkD3QwRLZPFhQxW/DrRYmOHfEnPhoVw== X-Received: by 2002:a17:907:7fa8:: with SMTP id qk40mr43860927ejc.445.1634726255459; Wed, 20 Oct 2021 03:37:35 -0700 (PDT) Received: from ?IPV6:2001:b07:6468:f312:c8dd:75d4:99ab:290a? ([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id e7sm1053267edk.3.2021.10.20.03.37.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 20 Oct 2021 03:37:34 -0700 (PDT) Message-ID: Date: Wed, 20 Oct 2021 12:37:32 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.1.0 Subject: Re: [PATCH v3 3/3] KVM: vCPU kick tax cut for running vCPU Content-Language: en-US To: Wanpeng Li Cc: Sean Christopherson , LKML , kvm , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel References: <1634631160-67276-1-git-send-email-wanpengli@tencent.com> <1634631160-67276-3-git-send-email-wanpengli@tencent.com> <24e67e43-c50c-7e0f-305a-c7f6129f8d70@redhat.com> <45fabf5a-96b5-49dc-0cba-55714ae3a4b5@redhat.com> From: Paolo Bonzini In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 20/10/21 12:02, Wanpeng Li wrote: >> +#ifdef CONFIG_PREEMPT_RCU >> + /* The cost of rcu_read_lock() is nontrivial for preemptable RCU. */ >> + if (!rcuwait_active(w)) >> + return ret; >> +#endif >> + >> + rcu_read_lock(); >> + >> task = rcu_dereference(w->task); >> if (task) >> ret = wake_up_process(task); >> >> (If you don't, rcu_read_lock is essentially preempt_disable() and it >> should not have a large overhead). You still need the memory barrier >> though, in order to avoid missed wakeups; shameless plug for my >> article athttps://lwn.net/Articles/847481/. > You are right, the cost of rcu_read_lock() for preemptable RCU > introduces too much overhead, do you want to send a separate patch? Yes, I'll take care of this. Thanks! Paolo