Date: Fri, 30 Jan 2015 09:58:34 -0500 From: John Baldwin <jhb@FreeBSD.org> To: Ryan Stone <rysto32@gmail.com> Cc: "svn-src-head@freebsd.org" <svn-src-head@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "src-committers@freebsd.org" <src-committers@freebsd.org> Subject: Re: svn commit: r277900 - head/sys/x86/x86 Message-ID: <54CB9C1A.5060602@FreeBSD.org> In-Reply-To: <CAFMmRNxaartbZZ875F_YF01L7nQ%2BLKcd%2BUnD0RJdbJ=m0x5jbQ@mail.gmail.com> References: <201501292041.t0TKfhAJ029429@svn.freebsd.org> <8728880.CZu0UL854D@ralph.baldwin.cx> <CAFMmRNxaartbZZ875F_YF01L7nQ%2BLKcd%2BUnD0RJdbJ=m0x5jbQ@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On 1/29/15 10:51 PM, Ryan Stone wrote: > On Thu, Jan 29, 2015 at 3:45 PM, John Baldwin <jhb@freebsd.org> wrote: >> Also, note that we always use the TSC as the cpu ticker, even if it is not the >> timecounter. Thus, if C2+ is enabled on the systems, the kernel idle threads >> will have an artificially low runtime since their idle time is not properly >> accounted for. This does not affect any other threads as only the idle >> threads "run" while the CPU is in C2+ with the TSC effectively paused. The >> new default means that the idle threads will now have the proper runtime, >> however. > > However in a VM environment this means that runtimes for all threads > can be very wrong (regardless of whether we enter C2 or lower or not). > I have a coworker looking at using kvmclock in preference to TSC for > the cpu ticker when the kvmclock is available. I think that is orthogonal to older Core 2 CPUs which the above mail was about. :) However, yes, that sounds sensible. You might want to talk to bryanv@. He has a branch in projects (projects/paravirt I think?) that provides a framework for hypervisor "drivers" that would be a good place to plug this into. -- John Baldwin
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?54CB9C1A.5060602>