Hi Daniel,
qihua wu wrote:
> Hi, All,
>
> Do we have entry point to tell us whether the IO performed bypass FS
> cache or not?
> Somebody said using dd to copy file using raw disk format such as dd
> if=/dev/dsk/... will bypass the FS cache but using dd to copy a
> normal file will NOT bypass the FS cache, I'd like to verify this. I
> am wondering whether Dtrace could help on this case.
If the I/O (specifically, read/write) is not going through a cache
from/to the disk,
the physio(9f) routine should be called. Take a look at the physio(9f)
man page.
So,
# dtrace -n 'physio:entry{}'
should fire on read/write calls that bypass any caching. Try this with
dd if=foo of=/dev/null count=10
where foo is the file. If physio() is not getting called, code above
the disk
driver is buffering the data (or someone has written a very different
disk driver...).
If you try dd with the raw device, you'll see physio(9f) getting called.
max
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