Messages in this thread | | | Date | Thu, 02 Apr 2009 22:54:58 -0400 | From | Jeff Garzik <> | Subject | Re: Linux 2.6.29 |
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Trenton D. Adams wrote: > On Thu, Apr 2, 2009 at 8:01 PM, Jeff Garzik <jeff@garzik.org> wrote: >> Linus Torvalds wrote: >> The most interesting thing I found: the SSD does 80 MB/s for the first ~1 >> GB or so, then slows down dramatically. After ~2GB, it is down to 32 MB/s. >> After ~4GB, it reaches a steady speed around 23 MB/s. > > Isn't that the kernel IO queue, and the dd averaging of transfer > speed? For example, once you hit the dirty ratio limit, that is when > it starts writing to disk. So, the first bit you'll see really fast > speeds, as it goes to memory, but it averages out over time to a > slower speed. As an example...
overwrite.c is a special program that does this, in a loop:
write(buffer-N) data to pagecache start buffer-N write-out to storage wait for buffer-(N-1) write-out to complete
It uses the sync_file_range() system call, which is like fsync() on steroids, wearing cool sunglasses.
Regards,
Jeff
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