[RFC][PATCH] vsyscall-gtod_B3 (0/3)

john stultz
2004-03-04T00:11:42Z

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