Re: [PATCH] speed up SATA
From: Timothy Miller
Date: Tue Mar 30 2004 - 10:39:23 EST
Jens Axboe wrote:
Here's a quickly done patch that attempts to adjust the value based on a
previous range of completed requests. It changes ->max_sectors to be a
hardware limit, adding ->optimal_sectors to be our max issued io target.
It is split on READ and WRITE. The target is to keep request execution
time under BLK_IORATE_TARGET, which is 50ms in this patch. read-ahead
max window is kept within a single request in size.
One question I have is about how you are determining optimal request
size. You are basing this on the _maximum_ performance of the device,
but there could be huge differences between min and max performance.
Would it be better to compute optimal based on worst-case performance?
Or averaged over time?
Idealy, we'd have a running average where one hit of worst-case will
have an impact, but if that happens only once, it'll drop out of the
average, and best-case events will be considered but tempered as well.
If we're going for real-time, then we want to avoid any latency over
50ms. In that case, we'd want to go based on worst-case, although it
would still be good to let, say, an occasional hardware glitch which had
slow response to not have permanent impact.
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