Messages in this thread | | | Date | Fri, 12 Jan 2018 02:11:51 +0300 | From | Alexey Dobriyan <> | Subject | Re: [RFC PATCH v2 6/6] x86/entry/pti: don't switch PGD on when pti_disable is set |
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> I initially tried getpid() which I found to be cached by glibc, but I > switched to write(-1, "a", 1) in the example in the cover letter and > the test for 3 million runs roughly climbs from 200 ms to 900 ms under > kvm (with PCID this time, I didn't retest without).
umask() is the fastest system call I think. Also who cares about glibc caching?
static inline int sys_umask(int mask) { int rv; asm volatile ( "syscall" : "=a" (rv) : "0" (95), "D" (mask) : "rcx", "r11", "cc", "memory" ); return rv; }
int main(void) { unsigned int i;
for (i = 0; i < (1U << 24); i++) { sys_umask(0); } return 0; }
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