linux-kernel - Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and clock

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Message-ID: <5629904A.2070400@imgtec.com>
Date:	Thu, 22 Oct 2015 18:41:30 -0700
From:	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>
To:	Markos Chandras <markos.chandras@...tec.com>,
	<linux-mips@...ux-mips.org>
CC:	Alex Smith <alex.smith@...tec.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and
 clock_gettime()

You can not use R4K CP0_count in SMP (multicore) without core-specific 
adjustment.
After first power-saving with core clock off or core down the values in 
CP0_count
in different cores are absolutely different.

Until you include in system a patch like 
http://patchwork.linux-mips.org/patch/10871/

     "MIPS: Setup an instruction emulation in VDSO protected page 
instead of user stack"

which creates a per-thread memory and put into that memory an adjustment 
value
(which can be changed during re-schedule to another core), the use of 
R4K counter is incorrect
in SMP environment.

Note: It is also possible to setup and maintain a per-core page with 
that value too as
an alternative variant for adjustment.
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