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From: Christophe Leroy <christophe.leroy@c-s.fr>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
	Paul Mackerras <paulus@samba.org>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [PATCH v3 2/8] powerpc/vdso32: Add support for CLOCK_{REALTIME/MONOTONIC}_COARSE
Date: Wed, 20 Nov 2019 16:17:41 +0100	[thread overview]
Message-ID: <20191120161741.Horde.zNDnbMKk_BJpkUOkWeRMsQ1@messagerie.si.c-s.fr> (raw)
In-Reply-To: <87eey2btxi.fsf@mpe.ellerman.id.au>

Michael Ellerman <mpe@ellerman.id.au> a écrit :

> Christophe Leroy <christophe.leroy@c-s.fr> writes:
>> This is copied and adapted from commit 5c929885f1bb ("powerpc/vdso64:
>> Add support for CLOCK_{REALTIME/MONOTONIC}_COARSE")
>> from Santosh Sivaraj <santosh@fossix.org>
>>
>> Benchmark from vdsotest-all:
>> clock-gettime-realtime: syscall: 3601 nsec/call
>> clock-gettime-realtime:    libc: 1072 nsec/call
>> clock-gettime-realtime:    vdso: 931 nsec/call
>> clock-gettime-monotonic: syscall: 4034 nsec/call
>> clock-gettime-monotonic:    libc: 1213 nsec/call
>> clock-gettime-monotonic:    vdso: 1076 nsec/call
>> clock-gettime-realtime-coarse: syscall: 2722 nsec/call
>> clock-gettime-realtime-coarse:    libc: 805 nsec/call
>> clock-gettime-realtime-coarse:    vdso: 668 nsec/call
>> clock-gettime-monotonic-coarse: syscall: 2949 nsec/call
>> clock-gettime-monotonic-coarse:    libc: 882 nsec/call
>> clock-gettime-monotonic-coarse:    vdso: 745 nsec/call
>>
>> Additional test passed with:
>> 	vdsotest -d 30 clock-gettime-monotonic-coarse verify
>
> This broke on 64-bit big endian, which uses the 32-bit VDSO, with errors
> like:
>
>   clock-gettime-monotonic-coarse/verify: 10 failures/inconsistencies  
> encountered
>   timestamp obtained from libc/vDSO not normalized:
>   	[-1574202155, 1061008673]
>   timestamp obtained from libc/vDSO predates timestamp
>   previously obtained from kernel:
>   	[74, 261310747] (kernel)
>   	[-1574202155, 1061008673] (vDSO)
>   timestamp obtained from libc/vDSO not normalized:
>   	[-1574202155, 1061008673]
>   timestamp obtained from libc/vDSO predates timestamp
>   previously obtained from kernel:
>   	[74, 261310747] (kernel)
>   	[-1574202155, 1061008673] (vDSO)
>   timestamp obtained from libc/vDSO not normalized:
>   	[-1574202155, 1061008673]
>   timestamp obtained from libc/vDSO predates timestamp
>   previously obtained from kernel:
>   	[74, 261310747] (kernel)
>   	[-1574202155, 1061008673] (vDSO)
>   timestamp obtained from libc/vDSO not normalized:
>   	[-1574202155, 1061008673]
>   timestamp obtained from libc/vDSO predates timestamp
>   previously obtained from kernel:
>   	[74, 261310747] (kernel)
>   	[-1574202155, 1061008673] (vDSO)
>   timestamp obtained from libc/vDSO not normalized:
>   	[-1574202155, 1061008673]
>   timestamp obtained from libc/vDSO predates timestamp
>   previously obtained from kernel:
>   	[74, 261310747] (kernel)
>   	[-1574202155, 1061008673] (vDSO)
>   Failure threshold (10) reached; stopping test.
>
>
> The diff below seems to fix it, but I'm not sure it's correct. ie. we
> just ignore the top part of the values, how does that work?

Your change makes sense, it is consistent with other functions using  
STAMP_XTIME.

It works because nanoseconds are max 999999999, it fits 32 bits regs.

Christophe


  reply	other threads:[~2019-11-20 15:17 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-29  9:53 [PATCH v3 0/8] powerpc/vdso32 enhancement and optimisation Christophe Leroy
2019-10-29  9:53 ` [PATCH v3 1/8] powerpc/32: Add VDSO version of getcpu on non SMP Christophe Leroy
2019-10-29  9:53 ` [PATCH v3 2/8] powerpc/vdso32: Add support for CLOCK_{REALTIME/MONOTONIC}_COARSE Christophe Leroy
2019-11-20 12:42   ` Michael Ellerman
2019-11-20 15:17     ` Christophe Leroy [this message]
2019-11-20 23:53       ` Michael Ellerman
2019-10-29  9:53 ` [PATCH v3 3/8] powerpc: Fix vDSO clock_getres() Christophe Leroy
2019-10-29  9:53 ` [PATCH v3 4/8] powerpc/vdso32: inline __get_datapage() Christophe Leroy
2019-11-22  1:58   ` Michael Ellerman
2019-11-22  6:38     ` Michael Ellerman
2019-11-27 14:47       ` Christophe Leroy
2019-11-28  5:31         ` Michael Ellerman
2019-12-02  8:02           ` Christophe Leroy
2019-10-29  9:53 ` [PATCH v3 5/8] powerpc/vdso32: Don't read cache line size from the datapage on PPC32 Christophe Leroy
2019-10-29  9:53 ` [PATCH v3 6/8] powerpc/vdso32: use LOAD_REG_IMMEDIATE() Christophe Leroy
2019-10-29  9:53 ` [PATCH v3 7/8] powerpc/vdso32: implement clock_getres entirely Christophe Leroy
2019-10-29  9:53 ` [PATCH v3 8/8] powerpc/vdso32: miscellaneous optimisations Christophe Leroy

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