• Anton Blanchard's avatar
    powerpc: Move 64bit VDSO to improve context switch performance · 30d0b368
    Anton Blanchard authored
    On 64bit applications the VDSO is the only thing in segment 0. Since the VDSO
    is position independent we can remove the hint and let get_unmapped_area pick
    an area. This will mean the vdso will be near other mmaps and will share
    an SLB entry:
    
    10000000-10001000 r-xp 00000000 08:06 5778459        /root/context_switch_64
    10010000-10011000 r--p 00000000 08:06 5778459        /root/context_switch_64
    10011000-10012000 rw-p 00001000 08:06 5778459        /root/context_switch_64
    fffa92ae000-fffa92b0000 rw-p 00000000 00:00 0
    fffa92b0000-fffa9453000 r-xp 00000000 08:06 4334051  /lib64/power6/libc-2.9.so
    fffa9453000-fffa9462000 ---p 001a3000 08:06 4334051  /lib64/power6/libc-2.9.so
    fffa9462000-fffa9466000 r--p 001a2000 08:06 4334051  /lib64/power6/libc-2.9.so
    fffa9466000-fffa947c000 rw-p 001a6000 08:06 4334051  /lib64/power6/libc-2.9.so
    fffa947c000-fffa9480000 rw-p 00000000 00:00 0
    fffa9480000-fffa94a8000 r-xp 00000000 08:06 4333852  /lib64/ld-2.9.so
    fffa94b3000-fffa94b4000 rw-p 00000000 00:00 0
    
    fffa94b4000-fffa94b7000 r-xp 00000000 00:00 0        [vdso] <----- here I am
    
    fffa94b7000-fffa94b8000 r--p 00027000 08:06 4333852  /lib64/ld-2.9.so
    fffa94b8000-fffa94bb000 rw-p 00028000 08:06 4333852  /lib64/ld-2.9.so
    fffa94bb000-fffa94bc000 rw-p 00000000 00:00 0
    fffe4c10000-fffe4c25000 rw-p 00000000 00:00 0        [stack]
    
    On a microbenchmark that bounces a token between two 64bit processes over pipes
    and calls gettimeofday each iteration (to access the VDSO), our context switch
    rate goes from 268k to 277k ctx switches/sec (tested on a 4GHz POWER6).
    Signed-off-by: default avatarAnton Blanchard <anton@samba.org>
    Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
    30d0b368
vdso.h 1.48 KB