From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f202.google.com (mail-pg1-f202.google.com [209.85.215.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A00353D4100 for ; Mon, 9 Mar 2026 15:36:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773070590; cv=none; b=Bdxt2gkpU9kVSxMp/wMr2IKHquzxtWe9ENk9zQtt7bEym/Kf0sJ2hDmTSwlEvu59bvqejAT5xUpZmHfc8rX1UmpMAsrwKpdz+QvlfzaiRbvbubud4u4U9PaOnKGSSgsCJlyadxFLCh0fMIEYB1hm+vp/UsMcz1w86PO00sJUl1A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773070590; c=relaxed/simple; bh=8STJekAaFwPzLSmMbD5LEd1DImwS08qunVsBresWQtI=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=skN6Vs61HjL6OdAr0cSBe4pKBHNlgBJIb/CRfTYN88HFdqqiSuHlLrjfwbUop6L8Wsin725zt8zJIK/c/FAFjqitHVBJ268xGkhiCjMbgNkYM8DHa8iDlSCB5XC4/hxIbOkRJlxDQzyjdDMiYcSVIupW3MvI1aOFbIzXzC8/AcY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=oCZco0nZ; arc=none smtp.client-ip=209.85.215.202 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="oCZco0nZ" Received: by mail-pg1-f202.google.com with SMTP id 41be03b00d2f7-c737b6686ddso3103176a12.3 for ; Mon, 09 Mar 2026 08:36:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1773070589; x=1773675389; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=z/VyzIuCqmA7zPKt1jhrtzJRnA3TqN016b76izXw4pE=; b=oCZco0nZ43jrwY+ZxAtyaVEEgTaXQMbp6lPi/CY/6WfJk+W77uh9L1EgxctynQwOgw FH5d1N0L8+22oieqZQmww/jnsmHq+LMhL4bPOwEodFcuqPFnE8CdoByj61a85ot6+bCR 3QnhpGQBCWkhUkJiXdMZyP8h7eXJYO7Nkyt54phWsckzgrHBNKlzRlMgbwee7xK5Btlm VKhNw7SQb18eHMnfYjcbtxuDPb4qGHKiqgfkKDP0ZzRPL1A/56WQWWSbvzNTrcvjgSKU uFrmx/9MArkuim/illB3+TRn51xaFBii7eAHC6wun3EoNmebNQ8tdJqKbBvOOmLqu/wI xDnQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1773070589; x=1773675389; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=z/VyzIuCqmA7zPKt1jhrtzJRnA3TqN016b76izXw4pE=; b=VtdqKh+EWoQoYTJUzeWtm/PQzQPo/oOGK3vzLg1NHI2XcAJ5PnRmKbK+HmnfBP53FN 3d6ADIMGXI3bp4a5ozfIsdDChaY5sxYNDqTheb5iOJJm7s3Bg5Lf+7W63rheKbRP472i HHQvf2J2RJSk/wN2o8/syum6XtYMzoDBO04+MA4gvjfGhZEZUTPDFQQgN+WEsAXKhhAZ 1vBCeeqFq2Mv1LmBUUyapEP+fetUHeMAxRPz1W0pZSgiEMNlg5A5nLtcVVRbo7vKwx+R B/IbLUez3zEZc/GduKX5GZFP2lKGi2f7Z+hqyZ5nQAHN1pYsdHHpPW+NrmVe9H4nJP+2 +GHg== X-Forwarded-Encrypted: i=1; AJvYcCVlMmslUVBVEZoloJbQYHFQnV21dSVII76A86kZfRFc5YYug5x2iNNbf3Rx0hTPEDLv/HOu5HGiPp+pkWs=@vger.kernel.org X-Gm-Message-State: AOJu0Yw1UgSRVxKunfogjx02vY7N4Og26JCpdRwSOPdDIk+taInh0am0 24THHeX6ImAuabP5wy+7snYqcfQu6tSGPoMbBDOfQKzKPWZhHvfvPHuVnY0LTIr1NaMNNi+9X7j ne4Ji9Q== X-Received: from pgbfe16.prod.google.com ([2002:a05:6a02:2890:b0:c73:9d90:977a]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a21:3289:b0:398:9820:f6de with SMTP id adf61e73a8af0-398982100e0mr2684067637.49.1773070588807; Mon, 09 Mar 2026 08:36:28 -0700 (PDT) Date: Mon, 9 Mar 2026 08:36:27 -0700 In-Reply-To: <20260309092132.2484-1-lirongqing@baidu.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260309092132.2484-1-lirongqing@baidu.com> Message-ID: Subject: Re: [PATCH] KVM: eventfd: Remove redundant synchronize_srcu_expedited from irqfd assignment From: Sean Christopherson To: lirongqing Cc: pbonzini@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Mon, Mar 09, 2026, lirongqing wrote: > From: Li RongQing > > The synchronize_srcu_expedited() call in kvm_irqfd_assign() is unnecessary > when adding a new irqfd to the resampler list. The list insertion is > already RCU-safe, and existing readers will either see the old or the > updated list without inconsistency. It's not required for kernel safety, but I do think it's required for KVM's ABI, e.g. to ensure the resampler is visible to readers before KVM_IRQFD returns to userspace. > Removing this call reduces latency during resampling irqfd setup. May I ask why you're micro-optimizing VMs with an in-kernel I/O APIC? > Signed-off-by: Li RongQing > --- > virt/kvm/eventfd.c | 1 - > 1 file changed, 1 deletion(-) > > diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c > index 3201f60..facfeab 100644 > --- a/virt/kvm/eventfd.c > +++ b/virt/kvm/eventfd.c > @@ -450,7 +450,6 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args) > } > > list_add_rcu(&irqfd->resampler_link, &irqfd->resampler->list); > - synchronize_srcu_expedited(&kvm->irq_srcu); > > mutex_unlock(&kvm->irqfds.resampler_lock); > } > -- > 2.9.4 >