21.05.2018 16:55, Roger Oberholtzer пишет:
I see the following write times when making a file:
# time dd if=/dev/zero of=file.txt count=2096576 bs=4096 2096576+0 records in 2096576+0 records out 8587575296 bytes (8.6 GB, 8.0 GiB) copied, 42.8592 s, 200 MB/s
real 0m45.338s user 0m0.526s sys 0m5.100s
# time dd if=/dev/zero of=file.txt count=1096576 bs=4096 1096576+0 records in 1096576+0 records out 4491575296 bytes (4.5 GB, 4.2 GiB) copied, 2.69905 s, 1.7 GB/s
real 0m2.708s user 0m0.333s sys 0m2.366s
What are values of /proc/sys/vm/dirty_ratio and dirty_bytes? And what is memory size?
The 8 GB is perhaps closer to what we are doing. We make files so that each is not over 2 GB. But the writing is sustained. Perhaps this is not a bad write speed. It is faster than the data rate. So we should be keeping up.
It is interesting that the disk sync time is not in either user or sys time for the 8 GB file. But as you can see from the real time, we still have to wait for it to happen.
I suspect this time is accounted as "IO wait" time mostly.
But something just ain't right. Time to review our application to see if something else has happened. We used to use an Intel library to compress JPEG buffers (memory -> memory). We now use Turbo JPEG to do the same. That seems to be as fast. But it is the only thing we have changed in the code. (Famous last words - but I did verify this in our revision control system.)
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