Hi,
I observed that one multi-threaded application is generating so many
cross-calls (xcalls) on my AMD multi-core machine. A snapshot of stack trace is
shown below. I think that this is because of "segvn" activity, i.e. unmapping
the page and generating cross-call activity to maintain MMU level coherence
across the processors (from the Solaris Internals book). I read that by
increasing segmap cache size, we can improve the performance of some
multi-threaded applications (which produce serious File IO). Using adb, I am
able to change the size of "segmap cache". However, we will get this benefit
only on the File systems other than ZFS. I have ZFS and also I am unable to
change the size of segvn. I don't know whether ZFS uses segvn cache or not.
However, I tried to change the size of segvn cache like segmap using adb, but
failed. It is giving the message as shown below.
$ pfexec adb -kw /dev/ksyms /dev/mem
physmem 7ff23f
segmapsize/D
segmapsize: 67108864
segvnsize/D
adb: failed to dereference symbol: unknown symbol name
Could anyone tell me how can I increase the size of segvn cache on my machine.
$ pfexec dtrace -n 'xcalls /execname=="my_multithreaded"/ {...@[stack()] =
count()}'
dtrace: description 'xcalls ' matched 2 probes
unix`xc_do_call+0x135
unix`xc_call+0x4b
unix`hat_tlb_inval+0x2af
unix`unlink_ptp+0x92
unix`htable_release+0xfa
unix`hat_unload_callback+0x1d8
genunix`segvn_unmap+0x255
genunix`as_unmap+0xf2
genunix`munmap+0x80
unix`sys_syscall32+0x101
377
unix`xc_do_call+0x135
unix`xc_call+0x4b
unix`hat_tlb_inval+0x2af
unix`x86pte_update+0x69
unix`hati_update_pte+0x10c
unix`hat_pagesync+0x169
genunix`pvn_getdirty+0x5d
zfs`zfs_putpage+0x1c7
genunix`fop_putpage+0x74
genunix`segvn_sync+0x137
genunix`as_ctl+0x200
genunix`memcntl+0x764
unix`sys_syscall32+0x101
946
unix`xc_do_call+0x135
unix`xc_call+0x4b
unix`hat_tlb_inval+0x2af
unix`unlink_ptp+0x92
unix`htable_release+0xfa
unix`hat_unload_callback+0x24a
genunix`segvn_unmap+0x255
genunix`as_unmap+0xf2
genunix`munmap+0x80
unix`sys_syscall32+0x101
2494
.........
....
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