From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59405) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1c6JCx-0004x5-W3 for qemu-devel@nongnu.org; Mon, 14 Nov 2016 10:30:13 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1c6JCu-0004FT-L9 for qemu-devel@nongnu.org; Mon, 14 Nov 2016 10:30:08 -0500 Received: from mx1.redhat.com ([209.132.183.28]:49366) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1c6JCu-0004FM-D5 for qemu-devel@nongnu.org; Mon, 14 Nov 2016 10:30:04 -0500 References: <1478711602-12620-1-git-send-email-stefanha@redhat.com> <5826231D.7070208@redhat.com> <20161114152642.GE26198@stefanha-x1.localdomain> From: Paolo Bonzini Message-ID: <90b5f81f-eab0-72dc-63b8-143477cb5286@redhat.com> Date: Mon, 14 Nov 2016 16:29:49 +0100 MIME-Version: 1.0 In-Reply-To: <20161114152642.GE26198@stefanha-x1.localdomain> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="9lKnEEej6wc97v1iPuIRA12gTw0njtRwU" Subject: Re: [Qemu-devel] [RFC 0/3] aio: experimental virtio-blk polling mode List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi , Karl Rister Cc: Stefan Hajnoczi , qemu-devel@nongnu.org, Andrew Theurer , Fam Zheng This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --9lKnEEej6wc97v1iPuIRA12gTw0njtRwU From: Paolo Bonzini To: Stefan Hajnoczi , Karl Rister Cc: Stefan Hajnoczi , qemu-devel@nongnu.org, Andrew Theurer , Fam Zheng Message-ID: <90b5f81f-eab0-72dc-63b8-143477cb5286@redhat.com> Subject: Re: [Qemu-devel] [RFC 0/3] aio: experimental virtio-blk polling mode References: <1478711602-12620-1-git-send-email-stefanha@redhat.com> <5826231D.7070208@redhat.com> <20161114152642.GE26198@stefanha-x1.localdomain> In-Reply-To: <20161114152642.GE26198@stefanha-x1.localdomain> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable On 14/11/2016 16:26, Stefan Hajnoczi wrote: > On Fri, Nov 11, 2016 at 01:59:25PM -0600, Karl Rister wrote: >> QEMU_AIO_POLL_MAX_NS IOPs >> unset 31,383 >> 1 46,860 >> 2 46,440 >> 4 35,246 >> 8 34,973 >> 16 46,794 >> 32 46,729 >> 64 35,520 >> 128 45,902 >=20 > The environment variable is in nanoseconds. The range of values you > tried are very small (all <1 usec). It would be interesting to try > larger values in the ballpark of the latencies you have traced. For > example 2000, 4000, 8000, 16000, and 32000 ns. >=20 > Very interesting that QEMU_AIO_POLL_MAX_NS=3D1 performs so well without= > much CPU overhead. That basically means "avoid a syscall if you already know there's something to do", so in retrospect it's not that surprising. Still interesting though, and it means that the feature is useful even if you don't have CPU to waste. Paolo --9lKnEEej6wc97v1iPuIRA12gTw0njtRwU Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQEcBAEBCAAGBQJYKdhyAAoJEL/70l94x66Do4cH/0neFJfQVSQSG6P5id55fa1I oAEtkejrtBYbyAc1LG9vl1jr863ThV5kTcsFloDPyAsJwEYcD8QCB6/wQd6oezm1 4CVrhTN5JNJIt86OZTRavnbNEWUAjKiU0pPgeBpS0wSaKMmDpyG0YtP3rtIK7PT+ FSkRWu2PiPUmHqyIwJ2oQbplUHk82d9/uwF05FKfO+L3YZOn/C2F+AjN2rPxWYAv pBEsF17ecWJJSYkyLDtqHzVK/s7+Cp7zgKTP1fpYWsQxQ/fXDh+V/qU+aJvBWjSm UkwhKohhd+9unQ8yLxXGAlO3dURgPPmbSZbxcLeXK/V5ZaficnIArD4NHsc4qgI= =2VOj -----END PGP SIGNATURE----- --9lKnEEej6wc97v1iPuIRA12gTw0njtRwU--