From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-171.mta0.migadu.com (out-171.mta0.migadu.com [91.218.175.171]) (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 22CEB216A1D for ; Thu, 24 Oct 2024 20:15:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.171 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729800904; cv=none; b=KUxTBL8fYRehHMKiH2cNLGu3xL8UouhgbewKTlphmGIeYZgXKLvXbLV7Hd++V5F+kh9/78WzbqhIGwl1SgerxqsgFY53MvGvzQAVVAca2vY34kZYxU1vJEjopzuuOOR0nlib1upM+ry/Djf70GX4aZCn+3K0smbi+7IV7zPsrEo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729800904; c=relaxed/simple; bh=6fj/q8BQSOINphdKPPLUDq7M+GfsWT/xgsFdcpeWwHs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=aCkrUNZAms6FZJIcNGXarX6LQDf9dxFrsuq0HTo1Md/TV3w67f63y0vwdKQy1tYFT77blDeFJMUhSYLoB0rfQWmJJ5S2Q5OPFX6aYVbp5k6+XoVmtcNXIXjdIHy6m3e7hRaRJRE4pWtfKKfSmmxKLXiHbuGQu7WlZorTS1OQSr4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=YfMBqlEu; arc=none smtp.client-ip=91.218.175.171 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="YfMBqlEu" Date: Thu, 24 Oct 2024 13:14:53 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1729800899; 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: in-reply-to:in-reply-to:references:references; bh=UtFndtJcIL3zsSxbBk4RRQ6rdE2RirToZ3JUO30TCHs=; b=YfMBqlEuY3d4sssErtWX/tyOE6MwT9DGBdAkTCuk3A3qClaZ1jgVMh94ystYpCwzOS3XQ0 kA6nAgW6nZsGBkOEUHBGkUp3x8C8S2QFSMgI7b/odoVduDw6c6fJO90OQ6BOTifEgTsS7k fKQmtIPOjE09rsN97IuRq5Y3IxznMxw= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Oliver Upton To: Marc Zyngier Cc: Zhiqiang Ni , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, wanghaibin.wang@huawei.com, tangnianyao@huawei.com, wangzhou1@hisilicon.com, yuzenghui@huawei.com, wangyanan55@huawei.com, jiangkunkun@huawei.com, jiaqingtong@huawei.com Subject: Re: [bug report] KVM: arm64: vgic-its: Performance degradation on GICv3 LPI injection Message-ID: References: <86y12e2amf.wl-maz@kernel.org> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <86y12e2amf.wl-maz@kernel.org> X-Migadu-Flow: FLOW_OUT On Thu, Oct 24, 2024 at 09:00:56AM +0100, Marc Zyngier wrote: > On Thu, 24 Oct 2024 06:06:58 +0100, > Zhiqiang Ni wrote: > > > > Hi all, > > > > I found a performance degradation on GICv3 LPI injection after this > > commit ad362fe07fecf0aba839ff2cc59a3617bd42c33f(KVM: arm64: vgic-its: > > Avoid potential UAF in LPI translation cache). > > > > In my testcase, the vm's configuration is 60 VCPU 120G RAM with a > > 32-queue NIC and the kernel version is 5.10. The number of new TCP > > connections per second changed from 150,000 to 50,000 after this > > patch, with the %sys of cpu changed from 15% to 85%. > > What is the VM running? How is the traffic generated? Without a > reproducer, I struggle to see how we are going to analyse this issue. > > We can't go back to the previous situation anyway, as it has been > shown that what we had before was simply unsafe (the commit message > explains why). > > > From the ftrace, I found that the duration of vgic_put_irq() is > > 13.320 us, which may be the reason for the performance degradation. > > > > The call stack looks like below: > > kvm_arch_set_irq_inatomic() > > vgic_has_its(); > > vgic_its_inject_cached_translation() > > vgic_its_check_cache() > > vgic_queue_irq_unlock() > > vgic_put_irq() > > Are you suggesting that it is the combination of vgic_get_irq_kref() + > vgic_irq_put() that leads to excessive latency? Both are essentially > atomic operations, which should be pretty cheap on a modern CPU > (anything with FEAT_LSE). Looks like the bug report is for a 5.10 kernel, and at that point in ancient history KVM takes the lpi_list_lock for every vgic_irq_get() / vgic_irq_put() The series below that we took upstream has the necessary improvements to alleviate lock contention, Zhiqiang you may want to consider backporting this into your kernel. https://lore.kernel.org/all/20240221054253.3848076-1-oliver.upton@linux.dev/ -- Thanks, Oliver