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Date: Fri, 08 May 2009 14:05:29 -0500 From: Anthony Liguori <anthony@...emonkey.ws> To: Gregory Haskins <ghaskins@...ell.com> CC: Avi Kivity <avi@...hat.com>, Chris Wright <chrisw@...s-sol.org>, Gregory Haskins <gregory.haskins@...il.com>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org Subject: Re: [RFC PATCH 0/3] generic hypercall support Gregory Haskins wrote: > Its more of an issue of execution latency (which translates to IO > latency, since "execution" is usually for the specific goal of doing > some IO). In fact, per my own design claims, I try to avoid exits like > the plague and generally succeed at making very few of them. ;) > > So its not really the .4% reduction of cpu use that allures me. Its the > 16% reduction in latency. Time/discussion will tell if its worth the > trouble to use HC or just try to shave more off of PIO. If we went that > route, I am concerned about falling back to MMIO, but Anthony seems to > think this is not a real issue. > It's only a 16% reduction in latency if your workload is entirely dependent on the latency of a hypercall. What is that workload? I don't think it exists. For a network driver, I have a hard time believing that anyone cares that much about 210ns of latency. We're getting close to the cost of a few dozen instructions here. Regards, Anthony Liguori -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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