From patchwork Tue Jan 28 14:00:06 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mauro Carvalho Chehab X-Patchwork-Id: 11354363 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 10A3114E3 for ; Tue, 28 Jan 2020 14:01:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E304F24688 for ; Tue, 28 Jan 2020 14:01:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1580220080; bh=a6mkRzjWhCmIHE9IUbkl8qYiPklT0cEDtjZ7TXoFbrE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=IJwklBi1qSf4FxPvXwgfr9bMMuOwNuKQFFLQrmZXJUX0HeEttl0cnLaOnBkQhP0v3 suJ+NI0bm2Yhvlku/LYekP7egsh+Zov0h0TIaw7/nLFRMbMTwrpFQTqTvrYg0n2LkK WXS9DY450f4mO1+sd/9hRcfsg088OumMQEHdAKho= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727395AbgA1OBP (ORCPT ); Tue, 28 Jan 2020 09:01:15 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:59306 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727297AbgA1OAq (ORCPT ); Tue, 28 Jan 2020 09:00:46 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=Sender:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=/9G2blGVWjqgR965RRc1wFm/0hKu3kd3si70pvH2CPo=; b=h3dKn3NPPEjfnXRXe/6ajZsD0D 91dZ0ibztBRd911ztaZtHOy6t76huzWm4uuaNsfVaQ0LtoxEDCFo3aWVH91Qvyo8HvUZDGST13iNC OgzIpUXrWvOlWISQdQIlYcQcJfdtRXW4/fCcFC45eR4peyJSpweBCsKWjgcFDZaIgKp+qGquYytzr 4WvNtNHzg4jgyj5eOrMTAROoE0VW9x4QTzSfUg6t4NzwF1gTRw7/xaHCDyVgZqAJl1PMc7Eo7iKVU xU2j5TIMiz3PvKTkdMtzs9MZP5QPEMUgJ7NLW0m4x2Gty6vgOFuCQWsuBBBs/tTWY5CsCi/P/YRnm kCqVv44Q==; Received: from [177.41.103.99] (helo=bombadil.infradead.org) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1iwRQ6-0007io-09; Tue, 28 Jan 2020 14:00:46 +0000 Received: from mchehab by bombadil.infradead.org with local (Exim 4.92.3) (envelope-from ) id 1iwRPp-001BNa-BR; Tue, 28 Jan 2020 15:00:29 +0100 From: Mauro Carvalho Chehab To: Linux Media Mailing List Cc: Mauro Carvalho Chehab , Mauro Carvalho Chehab , Paolo Bonzini , Jonathan Corbet , kvm@vger.kernel.org, linux-doc@vger.kernel.org Subject: [PATCH 05/27] docs: virt: convert halt-polling.txt to ReST format Date: Tue, 28 Jan 2020 15:00:06 +0100 Message-Id: X-Mailer: git-send-email 2.24.1 In-Reply-To: References: MIME-Version: 1.0 Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org - Fix document title to match ReST format - Convert the table to be properly recognized - Some indentation fixes to match ReST syntax. Signed-off-by: Mauro Carvalho Chehab --- .../{halt-polling.txt => halt-polling.rst} | 84 ++++++++++--------- Documentation/virt/kvm/index.rst | 1 + 2 files changed, 44 insertions(+), 41 deletions(-) rename Documentation/virt/kvm/{halt-polling.txt => halt-polling.rst} (64%) diff --git a/Documentation/virt/kvm/halt-polling.txt b/Documentation/virt/kvm/halt-polling.rst similarity index 64% rename from Documentation/virt/kvm/halt-polling.txt rename to Documentation/virt/kvm/halt-polling.rst index 4f791b128dd2..d8f7516bd8d9 100644 --- a/Documentation/virt/kvm/halt-polling.txt +++ b/Documentation/virt/kvm/halt-polling.rst @@ -1,3 +1,4 @@ +=========================== The KVM halt polling system =========================== @@ -68,7 +69,8 @@ steady state polling interval but will only really do a good job for wakeups which come at an approximately constant rate, otherwise there will be constant adjustment of the polling interval. -[0] total block time: the time between when the halt polling function is +[0] total block time: + the time between when the halt polling function is invoked and a wakeup source received (irrespective of whether the scheduler is invoked within that function). @@ -81,31 +83,32 @@ shrunk. These variables are defined in include/linux/kvm_host.h and as module parameters in virt/kvm/kvm_main.c, or arch/powerpc/kvm/book3s_hv.c in the powerpc kvm-hv case. -Module Parameter | Description | Default Value --------------------------------------------------------------------------------- -halt_poll_ns | The global max polling | KVM_HALT_POLL_NS_DEFAULT - | interval which defines | - | the ceiling value of the | - | polling interval for | (per arch value) - | each vcpu. | --------------------------------------------------------------------------------- -halt_poll_ns_grow | The value by which the | 2 - | halt polling interval is | - | multiplied in the | - | grow_halt_poll_ns() | - | function. | --------------------------------------------------------------------------------- -halt_poll_ns_grow_start | The initial value to grow | 10000 - | to from zero in the | - | grow_halt_poll_ns() | - | function. | --------------------------------------------------------------------------------- -halt_poll_ns_shrink | The value by which the | 0 - | halt polling interval is | - | divided in the | - | shrink_halt_poll_ns() | - | function. | --------------------------------------------------------------------------------- ++-----------------------+---------------------------+-------------------------+ +|Module Parameter | Description | Default Value | ++-----------------------+---------------------------+-------------------------+ +|halt_poll_ns | The global max polling | KVM_HALT_POLL_NS_DEFAULT| +| | interval which defines | | +| | the ceiling value of the | | +| | polling interval for | (per arch value) | +| | each vcpu. | | ++-----------------------+---------------------------+-------------------------+ +|halt_poll_ns_grow | The value by which the | 2 | +| | halt polling interval is | | +| | multiplied in the | | +| | grow_halt_poll_ns() | | +| | function. | | ++-----------------------+---------------------------+-------------------------+ +|halt_poll_ns_grow_start| The initial value to grow | 10000 | +| | to from zero in the | | +| | grow_halt_poll_ns() | | +| | function. | | ++-----------------------+---------------------------+-------------------------+ +|halt_poll_ns_shrink | The value by which the | 0 | +| | halt polling interval is | | +| | divided in the | | +| | shrink_halt_poll_ns() | | +| | function. | | ++-----------------------+---------------------------+-------------------------+ These module parameters can be set from the debugfs files in: @@ -117,20 +120,19 @@ Note: that these module parameters are system wide values and are not able to Further Notes ============= -- Care should be taken when setting the halt_poll_ns module parameter as a -large value has the potential to drive the cpu usage to 100% on a machine which -would be almost entirely idle otherwise. This is because even if a guest has -wakeups during which very little work is done and which are quite far apart, if -the period is shorter than the global max polling interval (halt_poll_ns) then -the host will always poll for the entire block time and thus cpu utilisation -will go to 100%. +- Care should be taken when setting the halt_poll_ns module parameter as a large value + has the potential to drive the cpu usage to 100% on a machine which would be almost + entirely idle otherwise. This is because even if a guest has wakeups during which very + little work is done and which are quite far apart, if the period is shorter than the + global max polling interval (halt_poll_ns) then the host will always poll for the + entire block time and thus cpu utilisation will go to 100%. -- Halt polling essentially presents a trade off between power usage and latency -and the module parameters should be used to tune the affinity for this. Idle -cpu time is essentially converted to host kernel time with the aim of decreasing -latency when entering the guest. +- Halt polling essentially presents a trade off between power usage and latency and + the module parameters should be used to tune the affinity for this. Idle cpu time is + essentially converted to host kernel time with the aim of decreasing latency when + entering the guest. -- Halt polling will only be conducted by the host when no other tasks are -runnable on that cpu, otherwise the polling will cease immediately and -schedule will be invoked to allow that other task to run. Thus this doesn't -allow a guest to denial of service the cpu. +- Halt polling will only be conducted by the host when no other tasks are runnable on + that cpu, otherwise the polling will cease immediately and schedule will be invoked to + allow that other task to run. Thus this doesn't allow a guest to denial of service the + cpu. diff --git a/Documentation/virt/kvm/index.rst b/Documentation/virt/kvm/index.rst index 488c6370a447..b39f4894b61d 100644 --- a/Documentation/virt/kvm/index.rst +++ b/Documentation/virt/kvm/index.rst @@ -9,6 +9,7 @@ KVM amd-memory-encryption cpuid + halt-polling vcpu-requests arm/index