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Re: [PATCH v2] x86/time: switch platform timer hooks to altcall
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 24 Feb 2022 15:41:57 +0100
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
- Delivery-date: Thu, 24 Feb 2022 14:42:17 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 24.02.2022 15:09, Roger Pau Monné wrote:
> On Thu, Jan 13, 2022 at 02:17:18PM +0100, Jan Beulich wrote:
>> Except in the "clocksource=tsc" case we can replace the indirect calls
>> involved in accessing the platform timers by direct ones, as they get
>> established once and never changed. To also cover the "tsc" case, invoke
>> what read_tsc() resolves to directly. In turn read_tsc() then becomes
>> unreachable and hence can move to .init.*.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Thanks.
>> ---
>> TBD: Instead of adding __init to read_tsc() we could also ditch the
>> function altogether, using a dedicated (non-canonical) pointer
>> constant instead for the .read_counter initializer and the two
>> comparisons done on plt_src.read_counter.
>
> I was going to suggest adding an ASSERT_UNREACHABLE, but not sure it
> makes much sense if the function is init only.
>
> I would be fine with using a non-canonical pointer.
I guess I'll put in the patch as is and do the conversion in a follow-up
change adding __initconst_cf_clobber (once it's clear what to do about
structures which are written to).
Jan
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