From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57416) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ejmkA-00019t-K0 for qemu-devel@nongnu.org; Thu, 08 Feb 2018 09:00:13 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ejmk7-0001fB-H4 for qemu-devel@nongnu.org; Thu, 08 Feb 2018 09:00:06 -0500 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:49036 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1ejmk7-0001e3-Cq for qemu-devel@nongnu.org; Thu, 08 Feb 2018 09:00:03 -0500 Date: Thu, 8 Feb 2018 09:00:00 -0500 From: Luiz Capitulino Message-ID: <20180208090000.3bfc5cd6@redhat.com> In-Reply-To: <20180208092928.GN20703@redhat.com> References: <20180207175014.11157-1-lcapitulino@redhat.com> <20180207175014.11157-3-lcapitulino@redhat.com> <20180208092928.GN20703@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH 2/2] qmp: document query-cpus performance issue List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Daniel P. =?UTF-8?B?QmVycmFuZ8Op?=" Cc: qemu-devel@nongnu.org, armbru@redhat.com, eblake@redhat.com, ehabkost@redhat.com, mihajlov@linux.vnet.ibm.com On Thu, 8 Feb 2018 09:29:28 +0000 Daniel P. Berrang=C3=A9 wrote: > On Wed, Feb 07, 2018 at 12:50:14PM -0500, Luiz Capitulino wrote: > > Signed-off-by: Luiz Capitulino > > --- > > qapi-schema.json | 4 ++++ > > 1 file changed, 4 insertions(+) > >=20 > > diff --git a/qapi-schema.json b/qapi-schema.json > > index 82d6f12b53..0665a14dba 100644 > > --- a/qapi-schema.json > > +++ b/qapi-schema.json > > @@ -526,6 +526,10 @@ > > # > > # Returns a list of information about each virtual CPU. > > # > > +# WARNING: This command incurs a performance penalty for latency > > +# sensitive workloads and hence it's not recommended to > > +# to be used in production. Use query-cpus-fast instead =20 >=20 > I suggest being more explicit about exactly what the problem is, so people > understand implications if they choose to still use it. ie I'll add your text. >=20 > This command causes vCPU threads to exit to userspace, which causes > an small interruption guest CPU execution. This will have a negative > impact on realtime guests and other latency sensitive guest workloads. > It is recommended to use query-cpus-fast instead of this command to > avoid the vCPU interruption. >=20 > Regards, > Daniel