Subject: [RFC][PATCH] vsyscall-gtod_B3 (0/3)
From: john stultz <johnstul@us.ibm.com>
To: lkml <linux-kernel@vger.kernel.org>
Cc: Andrea Arcangeli <andrea@suse.de>, Andi Kleen <ak@suse.de>,
       Ulrich Drepper <drepper@redhat.com>, Jamie Lokier <jamie@shareable.org>,
       "Martin J. Bligh" <mbligh@aracnet.com>,
       Wim Coekaerts <wim.coekaerts@oracle.com>,
       Joel Becker <Joel.Becker@oracle.com>, Chris McDermott <lcm@us.ibm.com>
Content-Type: text/plain
Message-Id: <1078359081.10076.191.camel@cog.beaverton.ibm.com>
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Date: Wed, 03 Mar 2004 16:11:22 -0800
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All,
	This is my port of the x86-64 vsyscall gettimeofday code to i386. This
patch moves gettimeofday into userspace, so it can be calledwithout the
syscall overhead, greatly improving performance. This is important for
any application, like a database, which heavily uses gettimeofday for
time-stamping. It supports both the TSC and IBM x44X cyclone time
source.
	
Example performance gain (using cyclone timesource):

int80 gettimeofday:
gettimeofday ( 1665576us / 1000000runs ) = 1.665574us

systenter gettimeofday:
gettimeofday ( 1239215us / 1000000runs ) = 1.239214us

vsyscall gettimeofday:
gettimeofday ( 875876us / 1000000runs ) = 0.875875us


I've broken the patch into three logical chuncks for clarity and to make
it easier to cherry pick the desired bits. 

o Part 1: Renames variables in timer_cyclone.c and timer_tsc.c to avoid
conflicts in the global namespace.
o Part 2: Core vsyscall-gtod implementation. 
o Part 3: vDSO hooks to avoid LD_PRELOADing or needing changes to glibc

Please let me know if you have any comments or suggestions.

thanks
-john

Existing issues:
----------------
o Bad pointers cause segfaults, rather then -EFAULT.

Release History:
----------------
B2 -> B3:
o Broke the patch up into 3 chunks
o Added vsyscall-int80.S hooks (4G disables SEP)

B1 -> B2:
o No LD_PRELOADing or changes to userspace required!
o removed hard-coded address in linker script

B0 -> B1:
o Cleaned up 4/4 split code, so no additional patch is needed.
o Fixed permissions on fixmapped cyclone pageo Improved
alternate_instruction workaround 
o Use NTP variables to avoid related time inconsistencieso minor code
cleanups

-
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