From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f201.google.com (mail-pg1-f201.google.com [209.85.215.201]) (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 9AB2C3C1995 for ; Mon, 9 Mar 2026 15:36:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773070591; cv=none; b=KRHsxZPdrQ6/VJrwADjHOoyPd8J+dRW+V4PT1zx7IUZG3d9d35nqD2Ss8e3PB9gGUvR5K2C5yVzKu432MQvwo9jF5orKtMPgnnT3fZgWv9V2U3LOFEWRqt3ki34duN092gZSjMdUHGrrUHH7FC7Aowy6ZykqfK0Qs0DVyGAKW6E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773070591; c=relaxed/simple; bh=8STJekAaFwPzLSmMbD5LEd1DImwS08qunVsBresWQtI=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=tYqIbpohWBhtcbZQ0MmqvqyrbQbt+YOT1/P5ZptyWkCnj2R3F8WVRlyRyJq2Iv5hLop3aylSf0F/ApJ8+854j9KWayba8GlfHCEnhFmZGaweKCzhqew9OaXz3bSPuqvAu/mka13rMyeO22dXa78gKf/vJx9Af/dyNrtIox7UjEM= 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=209.85.215.201 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-f201.google.com with SMTP id 41be03b00d2f7-c738563e61eso3212393a12.2 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=MoKHnPH88u7KuWB2p2ZyZ0NKmD8NBTIVEVFMDHAg3jHF1QtuSZP1POzBONbMzNCh99 x3lTb6GMWXlhKhu3E6JKX1dBTAHlWkki74vsN96dlVcS3KITbTPzmd0JTW6xRTeYciJi JuDDWJP3J82EJhVAngrm/tYL/EBRn9jcTQ8cgphHTOGvsU/wNLBfZOj2NMonfF8ekvxm 9tb7+BB9wnoBTYTMToKYnMaVXmD2+2twDWl+l/fUGWBREAAzC1oSA/h6ujl+GXOc6RGZ mYI4+X78nE2sJ+UwnsZZBJPuVzDHXSz9RY8BlkU0ADaThZnqHwfZcoqeNanqmeQFYzVj ADpQ== X-Forwarded-Encrypted: i=1; AJvYcCWfeX4A7pnpxS8H1HPXE0JQ1WYD2DGHaqPyxsS1+BONzjjY9exa3Tpsws++x1xviF9c3kg=@vger.kernel.org X-Gm-Message-State: AOJu0YwpVhJSQkCf6w1kcqR8c39TyWRCOniwMqkFI+yxvtymWnBle2mL q/PL1uId0+vfQn216q72TY3C82U9t+GGsWICQjzBviOGUBbpRv/WqBg/2TlBqq4Y+arA6iDgfRN NvBPk2A== 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: kvm@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 >