On Tue, 22 Dec 2009, Gregory Haskins wrote: > On 12/22/09 2:39 PM, Davide Libenzi wrote: > > On Tue, 22 Dec 2009, Gregory Haskins wrote: > > > >> 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 rejected > >> them on the grounds that they are only relevant to KVM. > > > > I thought we addressed this already, in the few hundreds of email we > > 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@xxxxxxxxxxxxxxx/2009-06/08548/Re:_[KVM-RFC_PATCH_1_2]_eventfd:_add_an_explicit_srcu_based_notifier_interface Didn't that ended up in schedule_work() being just fine, and no need was there for pre-emptible callbacks? > >> 2) it cannot retain the data field passed in the PIO. I wanted to have > >> one vector that could tell me what value was written, and this cannot be > >> expressed in ioeventfd. > > > > Like might have hinted in his reply, couldn't you add data support to the > > ioeventfd bits in KVM, instead of leaking them into mainline eventfd? > > > > 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. At that point, the KVM eventfd can take care of thing so that Michael bits do not break. - Davide -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
