>>> On 23.06.15 at 11:34, <andrew.coop...@citrix.com> wrote: > On 23/06/15 10:09, Jan Beulich wrote: >>>>> On 22.06.15 at 18:21, <david.vra...@citrix.com> wrote: >>> Since the NMI handler can now recognize watchdog NMIs, make >>> check_nmi_watchdog() only check for at least one watchdog NMI. This >>> prevents false negatives caused by other processors (which may be >>> being power managed by the BIOS) running at reduced clock frequencies. >> Doesn't this go a little too far, in that it allows through the case where >> an NMI works exactly once (a behavior not unheard of)? Lowering the >> count to e.g. 3 would seem acceptable, but not any further. Raising >> the wait time might then need to be the way to go if the (approximate) >> 1:3 ratio still isn't enough to cope with BIOS power managed CPUs. >> >> Btw., can an OS know of the power state CPUs come up in? I.e. can >> the wait time be adjusted dynamically? Or is this (perhaps intentionally) >> completely transparent to the OS? > > With the mwait driver, probably, as it is specifically designed to > completely bypass any firmware settings which might be in place.
The mwait driver deals with C states, while reduced frequency means P states (and we specifically busy wait here to prevent entering and C state). > Anything else is dependent on how much information can be gleaned from > the ACPI tables, but most firmware deliberately has a "BIOS controlled" > mode which is designed to restrict what the OS is capable of doing. None of which would help in identifying what state a CPU is in. Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
