On 05/02/2010 10:44 AM, Avi Kivity wrote: > On 05/02/2010 08:38 PM, Brian Gerst wrote: >> On Sun, May 2, 2010 at 10:53 AM, Avi Kivity<avi@xxxxxxxxxx> wrote: >> >>> The fpu code currently uses current->thread_info->status& TS_XSAVE as >>> a way to distinguish between XSAVE capable processors and older processors. >>> The decision is not really task specific; instead we use the task status to >>> avoid a global memory reference - the value should be the same across all >>> threads. >>> >>> Eliminate this tie-in into the task structure by using an alternative >>> instruction keyed off the XSAVE cpu feature; this results in shorter and >>> faster code, without introducing a global memory reference. >>> >> I think you should either just use cpu_has_xsave, or extend this use >> of alternatives to all cpu features. It doesn't make sense to only do >> it for xsave. >> > > I was trying to avoid a performance regression relative to the current > code, as it appears that some care was taken to avoid the memory reference. > > I agree that it's probably negligible compared to the save/restore > code. If the x86 maintainers agree as well, I'll replace it with > cpu_has_xsave. > I asked Suresh to comment on this, since he wrote the original code. He did confirm that the intent was to avoid a global memory reference. -hpa -- 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
