From: Cyrill Gorcunov <gorcunov@gmail.com>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
"H. Peter Anvin" <hpa@zytor.com>, Brian Gerst <brgerst@gmail.com>,
Jan Beulich <JBeulich@novell.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Frederic Weisbecker <fweisbec@gmail.com>
Subject: [Q x86-64] on kernel_eflags
Date: Tue, 5 Jul 2011 14:47:42 +0400 [thread overview]
Message-ID: <20110705104742.GO17941@sun> (raw)
While were looking into ret_from_fork code I somehow wondered
about the global kernel_eflags variable here.
arch/x86/cpu/common.c
---------------------
unsigned long kernel_eflags;
void __cpuinit cpu_init(void)
{
...
raw_local_save_flags(kernel_eflags);
}
arch/x86/kernel/entry_64.S
--------------------------
ENTRY(ret_from_fork)
DEFAULT_FRAME
LOCK ; btr $TIF_FORK,TI_flags(%r8)
pushq_cfi kernel_eflags(%rip)
popfq_cfi # reset kernel eflags
Every call to cpu_init renew global kernel_eflags
and every task switching does use this variable in a
sake of cleaning carry bit of flags register as far as
I can tell.
Should not every cpu has own copy of kernel_eflags? Just
to be consistent in style? Or this would be space waisting
and an optimization is done here?
Cyrill
next reply other threads:[~2011-07-05 10:47 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-05 10:47 Cyrill Gorcunov [this message]
2011-07-05 11:00 ` [Q x86-64] on kernel_eflags Ian Campbell
2011-07-05 11:15 ` Cyrill Gorcunov
2011-07-05 13:00 ` [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit Ian Campbell
2011-07-05 13:28 ` Cyrill Gorcunov
2011-07-06 9:25 ` Ian Campbell
2011-07-06 9:46 ` Cyrill Gorcunov
2011-07-06 9:57 ` Ian Campbell
2011-07-06 10:12 ` Cyrill Gorcunov
2011-07-06 9:39 ` Pekka Enberg
2011-07-06 23:17 ` Andi Kleen
2011-07-07 0:00 ` H. Peter Anvin
2011-07-05 13:00 ` [PATCH 2/3] x86: make 64 bit ret_from_fork a little more similar to 32 bit Ian Campbell
2011-07-06 9:41 ` Pekka Enberg
2011-07-05 13:00 ` [PATCH 3/3] x86: ret_from_fork: use symbolic contants for bits in EFLAGS Ian Campbell
2011-07-06 9:36 ` Pekka Enberg
2011-07-05 17:47 ` [Q x86-64] on kernel_eflags H. Peter Anvin
2011-07-05 17:56 ` Cyrill Gorcunov
2011-07-06 9:25 ` Ian Campbell
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