While the introduction of __copy_from_user_nocache (see commit:
0812a579c9) may have been an improvement
for sufficiently large writes, there is evidence to show that it is
deterimental for small writes. Unixbench's fstime test gives the
following results for 256 byte writes with MAX_BLOCK of 2000:
2.6.29-rc6 ( 5 samples, each in KB/sec ):
283750, 295200, 294500, 293000, 293300
2.6.29-rc6 + this patch (5 samples, each in KB/sec):
313050, 3106750, 293350, 306300, 307900
2.6.18
395700, 342000, 399100, 366050, 359850
See w_test() in src/fstime.c in unixbench version 4.1.0. Basically, the above test
consists of counting how much we can write in this manner:
alarm(10);
while (!sigalarm) {
for (f_blocks = 0; f_blocks < 2000; ++f_blocks) {
write(f, buf, 256);
}
lseek(f, 0L, 0);
}
Note, there are other components to the write syscall regression
that are not addressed here.
Signed-off-by: Salman Qazi <sqazi@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
__copy_from_user() will return invalid value 16 when it fails to
access user space and the size is 10.
Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Change header guards named "ASM_X86__*" to "_ASM_X86_*" since:
a. the double underscore is ugly and pointless.
b. no leading underscore violates namespace constraints.
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
