Comment 12 for bug 654764

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Tyler Hicks (tyhicks) wrote : Re: [Bug 654764] Re: writing to ecryptfs partition on SSD drive is many times slower than writing to unencrypted partition on the same drive

On Fri Jan 28, 2011 at 03:18:38AM -0000, Dustin Kirkland <email address hidden> wrote:
> time dd if=/dev/zero of=~/dummy bs=512 count=10240

There are a couple issues here:

1. eCryptfs currently implements a write-through cache. This means that
   reads are cached, but writes are not. There's currently someone
   investigating a switch to a proper write-back cache on files opened
   without the O_SYNC flag. This would result in writes being cached
   and, more importantly, write() returning before the page is
   encrypted. Some rough, initial tests show a very nice improvement.

2. bs=512 results in a 4 writes to a single page, meaning that single
   page is encrypted 4 times in a row and dd has to wait on the page
   encryption and writing 4096 bytes to the lower filesystem every
   time. This is why doing what I talked about in #1 has so much
   potential to increase performance.

Encryption isn't free, but we should be a little smarter about when we
do it.