On 05/06/2015 09:58 PM, Srinivasa Chamarthy wrote:
Thanks Eaton. One question thought. From the man page for refill_buffers:
"If this option is given, fio will refill the IO buffers on every
submit. The default is to only fill it at init time and reuse that
data. Only makes sense if zero_buffers isn't specified, naturally. If
data verification is enabled, refill_buffers is also automatically
enabled."
Every IO submitted will have a new pattern for repeated workloads?
using refill_buffers, i seem to get same pattern repeatedly. Is that
how it should be? i was under the impression that refill will use new
pattern every time.
# fio --filename=test_refill --readwrite=randwrite --size=1m
--refill_buffers --bs=256k --norandommap --name=refill
# for each in {0..3}; do dd if=test_refill bs=262144 count=1
skip=$each 2>/dev/null | md5sum; done
86c3e47e173a58ad93470fd8db856f8c -
6fe5ce86d04522889c99809d6d97cb94 -
9113ce00f3781861afc41aaf6da32428 -
f0b575c40e9da23b524f585723cbea4e -
# fio --filename=test_refill --readwrite=randwrite --size=1m
--refill_buffers --bs=256k --norandommap --name=refill
# for each in {0..3}; do dd if=test_refill bs=262144 count=1
skip=$each 2>/dev/null | md5sum; done
86c3e47e173a58ad93470fd8db856f8c -
6fe5ce86d04522889c99809d6d97cb94 -
9113ce00f3781861afc41aaf6da32428 -
f0b575c40e9da23b524f585723cbea4e -
First of all, please stop top posting. It breaks the flow of conversations.
Secondly, this is expected behavior, and it's done to get identical
behavior between runs. If you had longer runs, each buffer would be
different. But if you did a new run after that, the sequence of buffers
would be the same. Same thing happens with the offsets generated, the
buffer lengths generated, etc.
If you want a truly different run everytime, you have a few options. One
is to simply set randrepeat=0, then OS entropy will seed the random
generators. Or you can use randseed= to set a specific seed, which would
allow you to reproduce a specific run.
--
Jens Axboe
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