Re: Bad SSD performance with recent kernels

[Eric Dumazet]

Le dimanche 29 janvier 2012 Ã 19:16 +0800, Wu Fengguang a Ãcrit :


> Note that as long as buffered read(2) is used, it makes almost no
> difference (well, at least for now) to do "dd bs=128k" or "dd bs=2MB":
> the 128kb readahead size will be used underneath to submit read IO.
> 

Hmm...

# echo 3 >/proc/sys/vm/drop_caches ;dd if=/dev/sda of=/dev/null bs=128k count=32768
32768+0 enregistrements lus
32768+0 enregistrements Ãcrits
4294967296 octets (4,3 GB) copiÃs, 20,7718 s, 207 MB/s


# echo 3 >/proc/sys/vm/drop_caches ;dd if=/dev/sda of=/dev/null bs=2M count=2048
2048+0 enregistrements lus
2048+0 enregistrements Ãcrits
4294967296 octets (4,3 GB) copiÃs, 27,7824 s, 155 MB/s



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