From: vdso@mailbox.org
To: Naman Jain <namjain@linux.microsoft.com>
Cc: glx@kernel.org, mingo@redhat.com, bp@alien8.de,
dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com,
decui@microsoft.com, yunhong.jiang@linux.intel.com,
ricardo.neri-calderon@linux.intel.com,
rahul.tanwar@linux.intel.com, linux-kernel@vger.kernel.org,
linux-hyperv@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH] x86/init: Initialize wall clock in get_rtc_noop()
Date: Fri, 18 Sep 2026 21:11:50 -0700 (PDT) [thread overview]
Message-ID: <15750262.186413.1789791110042@app.mailbox.org> (raw)
In-Reply-To: <210aa40c-88e1-4d88-ba6b-9224b05b0820@linux.microsoft.com>
> On 09/14/2026 4:31 AM PDT Naman Jain <namjain@linux.microsoft.com> wrote:
>
>
> On 9/12/2026 9:05 AM, Roman Kisel wrote:
> > On Mon, Aug 31, 2026 at 08:25:28AM +0000, Naman Jain wrote:
[...]
> >> +void get_rtc_noop(struct timespec64 *now) { *now = (struct timespec64){0}; }
> >
> > Hi Naman,
> >
> > Could be
> >
> > *now = (struct timespec64){};
> >
> > to save a byte :)
>
> hi Roman,
> Thanks for reviewing.
>
> Tianyu pointed out offline that this is handled in yet another way in
> jailhouse code:
>
> arch/x86/kernel/jailhouse.c
> static void jailhouse_get_wallclock(struct timespec64 *now)
> {
> memset(now, 0, sizeof(now));
> }
Appreciate sharing! Makes sense to me, looks way more explicit. Most
importantly imo, the memset isn't actually producing a call here so
the clock no-op stays cheap when choosing `memset` over ` = {}`.
One can see that the kernel build compiles ` = {0}`, ` = {}` into
pxor ...
movups ...
on x64 in the above. I made sure the memset "call" is relaxed/optimized
away into the same sequence `pxor ...; movups ...`.
>
> Regards,
> Naman
>
> >
> > LGTM.
> > Reviewed-by: Roman Kisel <vdso@mailbox.org>
> >
> >>
> >> static __initconst const struct of_device_id of_cmos_match[] = {
> >> { .compatible = "motorola,mc146818" },
> >> --
> >> 2.43.0
> >>
prev parent reply other threads:[~2026-09-19 4:11 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-31 8:25 [PATCH] x86/init: Initialize wall clock in get_rtc_noop() Naman Jain
2026-09-09 18:42 ` Dexuan Cui
2026-09-11 4:23 ` Hardik Garg
2026-09-12 3:35 ` Roman Kisel
2026-09-14 11:31 ` Naman Jain
2026-09-19 4:11 ` vdso [this message]
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