From: "Jan Beulich" <JBeulich@suse.com> To: Joao Martins <firstname.lastname@example.org> Cc: Andrew Cooper <email@example.com>, Dario Faggioli <firstname.lastname@example.org>, Wei Liu <email@example.com>, xen-devel <firstname.lastname@example.org> Subject: Re: [PATCH] x86/time: use correct (local) time stamp in constant-TSC calibration fast path Date: Fri, 10 Jun 2016 00:59:22 -0600 [thread overview] Message-ID: <575A816A02000078000F3D4D@prv-mh.provo.novell.com> (raw) In-Reply-To: <5759B318.email@example.com> >>> On 09.06.16 at 20:19, <firstname.lastname@example.org> wrote: > [changing Dario address to citrix.com as it was bouncing for me ] > > On 06/09/2016 04:52 PM, Jan Beulich wrote: >>>>> On 09.06.16 at 17:00, <email@example.com> wrote: >>> On 06/09/2016 01:57 PM, Jan Beulich wrote: >>>>>>> On 09.06.16 at 14:11, <firstname.lastname@example.org> wrote: >>>> So in effect for the fast path the patch >>>> changes the situation from c->stime_local_stamp being effectively >>>> unused to c->stime_master_stamp being so. In the former case, if >>>> that really hadn't been a typo, deleting the write of that field from >>>> time_calibration_std_rendezvous() would have made sense, as >>>> get_s_time() certainly is more overhead than the simply memory >>>> read and write needed for keeping c->stime_master_stamp up to >>>> date (despite not being used). >>> I agree, but what I meant previously was more of a concern meaning: CPU 0 is > >>> doing an >>> expensive read_platform_time (e.g. HPET supposedly microseconds order, plus >>> a >>> non-contented lock) to set stime_master_stamp that doesn't get used at all - >>> effectively not using the clocksource set initially at boot. >> >> Yeah, there's likely some cleanup potential here, but of course we >> need to be pretty careful about not doing something that may be >> needed by some code paths but not others. But if you think you >> can help the situation without harming maintainability, feel free to >> go ahead. >> > OK, Makes sense. I'll likely do already so of it on my related series. Actually, since local time gets seeded from platform time in init_percpu_time(), I don't think we can do away with maintaining platform time. Jan _______________________________________________ Xen-devel mailing list Xenemail@example.com http://lists.xen.org/xen-devel
next prev parent reply other threads:[~2016-06-10 6:59 UTC|newest] Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-06-09 12:01 Jan Beulich 2016-06-09 12:10 ` Andrew Cooper 2016-06-09 12:11 ` Joao Martins 2016-06-09 12:57 ` Jan Beulich 2016-06-09 15:00 ` Joao Martins 2016-06-09 15:52 ` Jan Beulich 2016-06-09 18:19 ` Joao Martins 2016-06-10 6:59 ` Jan Beulich [this message] 2016-06-10 9:29 ` Jan Beulich 2016-06-10 17:07 ` Joao Martins 2016-06-09 12:12 ` Wei Liu
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