linux-kernel - Re: 2.6.21-rc5-mm1

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Date:	Tue, 27 Mar 2007 23:29:34 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Badari Pulavarty <pbadari@...il.com>,
	lkml <linux-kernel@...r.kernel.org>, Andi Kleen <ak@...e.de>
Subject: Re: 2.6.21-rc5-mm1

Andrew Morton a écrit :
> 
> The wheel spins around, slows then settles on.... 
> time-smp-friendly-alignment-of-struct-clocksource.patch!
> 
> Presumably because the ____cacheline_aligned made vsyscall_gtod_data_t get
> too big.  Or something.

Very strange, since here I have plenty of available room (256 bytes) :

ffffffffff600000 T vgettimeofday
ffffffffff60004e t vsysc2
ffffffffff600140 t vread_hpet
ffffffffff600150 t vread_tsc
ffffffffff600180 D __vsyscall_gtod_data
ffffffffff600280 D __vgetcpu_mode
ffffffffff6002c0 D __jiffies
<lot of space (256 bytes)>
ffffffffff600400 T vtime
ffffffffff600413 t vsysc1
ffffffffff600800 T vgetcpu
ffffffffff600c00 T venosys_1

It must depends on the compiler, and/or CONFIG_XXX options...

Anyway, I think we can safely move __vgetcpu_mode & __jiffies to the 1024 
bytes area dedicated to vgetcpu() implementation. This saves 128 bytes from 
vsyscall_0 area.

Could we add this patch instead of dropping 
time-smp-friendly-alignment-of-struct-clocksource.patch ?

Thank you

[PATCH] x86_64 : move __vgetcpu_mode & __jiffies  to the vsyscall_2 zone

We apparently hit the 1024 limit of vsyscall_0 zone when some debugging 
options are set, or if __vsyscall_gtod_data is 64 bytes larger.

In order to save 128 bytes from the vsyscall_0 zone, we move __vgetcpu_mode & 
__jiffies to vsyscall_2 zone where they really belong, since they are used 
only from vgetcpu() (which is in this vsyscall_2 area).

After patch is applied, new layout is :

ffffffffff600000 T vgettimeofday
ffffffffff60004e t vsysc2
ffffffffff600140 t vread_hpet
ffffffffff600150 t vread_tsc
ffffffffff600180 D __vsyscall_gtod_data
ffffffffff600400 T vtime
ffffffffff600413 t vsysc1
ffffffffff600800 T vgetcpu
ffffffffff600870 D __vgetcpu_mode
ffffffffff600880 D __jiffies
ffffffffff600c00 T venosys_1

Signed-off-by: Eric Dumazet <dada1@...mosbay.com>

View attachment "x86_64_vmlinux_lds.patch" of type "text/plain" (879 bytes)