lkml.org 
[lkml]   [2004]   [Feb]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: ext2/3 performance regression in 2.6 vs 2.4 for small interl

On 12-Feb-2004 Andrea Arcangeli wrote:

> the main difference is that 2.4 isn't in function of time, it's in
> function of requests, no matter how long it takes to write a request,
> so it's potentially optimizing slow devices when you don't care about
> latency (deadline can be tuned for each dev via
> /sys/block/*/queue/iosched/).

IMHO it's the opposite. Transfer speed * seek time of some
slow devices is lower than fast devices. For example:

Hard disk raw speed= 40MB/s seek time = 8ms
MO/ZIP raw speed= 3MB/s seek time = 25ms

One seek of HD costs about 320KB, while on a slow drive it's
only 75KB. 2.4 has a terrible latency on slow devices, and it
has very small advantage in terms of speed. On CDs and DVDs
the cost of a seek is much higher, but since the data is
usually accessed sequentially you have the high latency
penalty with no appreciable speed gain in this case too.


--
Giuliano.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 14:00    [from the cache]
©2003-2011 Jasper Spaans