From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gregory Haskins Subject: Re: [Alacrityvm-devel] [KVM PATCH v2 1/2] KVM: export lockless GSI attribute Date: Wed, 28 Oct 2009 09:19:54 -0400 Message-ID: <4AE844FA.4070408@gmail.com> References: <20091023023512.3891.65889.stgit@dev.haskins.net> <20091023023845.3891.36857.stgit@dev.haskins.net> <4AE460F4.2090905@redhat.com> <4AE5A336.4010801@gmail.com> <4AE5C26A.9000400@gmail.com> <4AE81710.1080103@redhat.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigBCCB9C62ECE66C2D1977AE6D" Cc: Gregory Haskins , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, alacrityvm-devel@lists.sourceforge.net To: Avi Kivity Return-path: In-Reply-To: <4AE81710.1080103@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigBCCB9C62ECE66C2D1977AE6D Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Avi Kivity wrote: > On 10/26/2009 05:38 PM, Gregory Haskins wrote: >>>> Instead of a lockless attribute, how about a ->set_atomic() method. = >>>> For >>>> msi this can be the same as ->set(), for non-msi it can be a functio= n >>>> that schedules the work (which will eventually call ->set()). >>>> >>>> The benefit is that we make a decision only once, when preparing the= >>>> routing entry, and install that decision in the routing entry >>>> instead of >>>> making it again and again later. >>>> =20 >>> Yeah, I like this idea. I think we can also get rid of the custom >>> workqueue if we do this as well, TBD. >>> =20 >> So I looked into this. It isn't straight forward because you need to >> retain some kind of state across the deferment on a per-request basis >> (not per-GSI). Today, this state is neatly tracked into the irqfd >> object itself (e.g. it knows to toggle the GSI). >> =20 >=20 > Yes, and it also contains the work_struct. >=20 > What if we make the work_struct (and any additional state) part of the > set_atomic() argument list? Does it simplify things? Hmmm, that might not, but we could do a kmalloc(GFP_ATOMIC) for such parameters. Considering this is just a safety net, perhaps this would work fine. >=20 >> So while generalizing this perhaps makes sense at some point, especial= ly >> if irqfd-like interfaces get added, it probably doesn't make a ton of >> sense to expend energy on it ATM. It is basically a generalization of= >> the irqfd deferrment code. Lets just wait until we have a user beyond= >> irqfd for now. Sound acceptable? >> =20 >=20 > I'll look at v3, but would really like to disentangle this. Ok, I will see what I can do. I need at least a v4 to get rid of the dependency on the now defunct v3:1/3 patch per yesterdays discussion. Kind Regards, -Greg --------------enigBCCB9C62ECE66C2D1977AE6D Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG/MacGPG2 v2.0.11 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkroRPoACgkQP5K2CMvXmqESvgCeKDKCD2U0IkxPzb4TWlm3ov8J sDYAn3OV5rbvGQ6oV0QmV20SbeOYfDp6 =FG05 -----END PGP SIGNATURE----- --------------enigBCCB9C62ECE66C2D1977AE6D--