AU: Speed up updates by using buffered writes.

AU: Speed up updates by using buffered writes.

Given that SSD writes are really slow, this improves performance significantly.
This reduces update time on AGZ from 375 to 100 seconds.

BUG=6901
TEST=unit tests, gmerged on device and measured speed

Change-Id: Idac7743f6eaa8f26878a2d1f6b9401513e2ca600

Committed: http://chrome-svn/viewvc/chromeos?view=rev&revision=e971f33

[adlr, 2010-09-22 20:44:52]

can you add a TODO to split DirectFileWriter into a BufferedFileWriter and old
fasioned DirectFileWriter?

LGTM if you address my request for another test

http://codereview.chromium.org/3471006/diff/1/4
File file_writer_unittest.cc (right):

http://codereview.chromium.org/3471006/diff/1/4#newcode1
file_writer_unittest.cc:1: // Copyright (c) 2010 The Chromium OS Authors. All
rights reserved.
how about a test that the buffering works? as in, write less than the buffer and
see no bytes in the file, then overflow the buffer and see some...

[petkov, 2010-09-22 23:07:27]

Switched to BufferedFileWriter and added separate unit tests.

PTAL

[adlr, 2010-09-22 23:32:44]

LGTM w/ nits

thanks!

http://codereview.chromium.org/3471006/diff/5001/6002
File buffered_file_writer.cc (right):

http://codereview.chromium.org/3471006/diff/5001/6002#newcode47
buffered_file_writer.cc:47: ssize_t rc_write = WriteBuffer();
it's a little weird if we have no buffered data, but should be okay

[petkov, 2010-09-22 23:50:43]

Empty buffers are not sent to the next FileWriter any more. Added appropriate
unit tests.

Pushing...

http://codereview.chromium.org/3471006/diff/5001/6002
File buffered_file_writer.cc (right):

http://codereview.chromium.org/3471006/diff/5001/6002#newcode47
buffered_file_writer.cc:47: ssize_t rc_write = WriteBuffer();
On 2010/09/22 23:32:44, adlr wrote:
> it's a little weird if we have no buffered data, but should be okay

Added a guard in WriteBuffer so that empty buffers are not sent to the next
FileWriter.