From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gregory Haskins Subject: Re: [GIT PULL] AlacrityVM guest drivers for 2.6.33 Date: Tue, 22 Dec 2009 14:53:14 -0500 Message-ID: <4B3123AA.8040205@gmail.com> References: <4B1D4F29.8020309@gmail.com> <20091218215107.GA14946@elte.hu> <4B2F9582.5000002@gmail.com> <20091222075742.GB26467@elte.hu> <4B3103B4.4070708@gmail.com> <4B3115C1.4070303@redhat.com> <4B311ADA.4000700@gmail.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig6BEE5224B97AF759C77EB7E8" Cc: Avi Kivity , Ingo Molnar , kvm@vger.kernel.org, Andrew Morton , torvalds@linux-foundation.org, "linux-kernel@vger.kernel.org" , netdev@vger.kernel.org, "alacrityvm-devel@lists.sourceforge.net" To: Davide Libenzi Return-path: In-Reply-To: Sender: kvm-owner@vger.kernel.org List-Id: netdev.vger.kernel.org This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig6BEE5224B97AF759C77EB7E8 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 12/22/09 2:39 PM, Davide Libenzi wrote: > On Tue, 22 Dec 2009, Gregory Haskins wrote: >=20 >> On 12/22/09 1:53 PM, Avi Kivity wrote: >>> I asked why the irqfd/ioeventfd mechanisms are insufficient, and you = did not reply. >>> >> >> BTW: the ioeventfd issue just fell through the cracks, so sorry about >> that. Note that I have no specific issue with irqfd ever since the >> lockless IRQ injection code was added. >> >> ioeventfd turned out to be suboptimal for me in the fast path for two >> reasons: >> >> 1) the underlying eventfd is called in atomic context. I had posted >> patches to Davide to address that limitation, but I believe he rejecte= d >> them on the grounds that they are only relevant to KVM. >=20 > I thought we addressed this already, in the few hundreds of email we=20 > exchanged back then :) We addressed the race conditions, but not the atomic callbacks. I can't remember exactly what you said, but the effect was "no", so I dropped it.= ;) This was the thread. http://www.archivum.info/linux-kernel@vger.kernel.org/2009-06/08548/Re:_[= KVM-RFC_PATCH_1_2]_eventfd:_add_an_explicit_srcu_based_notifier_interface= >=20 >=20 >=20 >> 2) it cannot retain the data field passed in the PIO. I wanted to hav= e >> one vector that could tell me what value was written, and this cannot = be >> expressed in ioeventfd. >=20 > Like might have hinted in his reply, couldn't you add data support to t= he=20 > ioeventfd bits in KVM, instead of leaking them into mainline eventfd? >=20 Perhaps, or even easier I could extend xinterface. Which is what I did ;= ) The problem with the first proposal is that you would no longer actually have an eventfd based mechanism...so any code using ioeventfd (like Michael Tsirkin's for instance) would break. Kind Regards, -Greg --------------enig6BEE5224B97AF759C77EB7E8 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/ iEYEARECAAYFAksxI6oACgkQP5K2CMvXmqFyggCfbUVH1csVX9xmLrU2Hx47KEIr 4AcAnRX32LyUqFlGex4HTp1poudYaUmo =rZ6D -----END PGP SIGNATURE----- --------------enig6BEE5224B97AF759C77EB7E8--