lkml.org 
[lkml]   [2006]   [Oct]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH] block layer: ioprio_best function fix
Currently ioprio_best function first checks wethere aioprio or bioprio equals
IOPRIO_CLASS_NONE (ioprio_valid() macros does that) and if it is so it returns
bioprio/aioprio appropriately. Thus the next four lines, that set aclass/bclass
to IOPRIO_CLASS_BE, if aclass/bclass == IOPRIO_CLASS_NONE, are never executed.

The second problem: if aioprio from class IOPRIO_CLASS_NONE and bioprio from
class IOPRIO_CLASS_IDLE are passed to ioprio_best function, it will return
IOPRIO_CLASS_IDLE. It means that during __make_request we can merge two
requests and set the priority of merged request to IDLE, while one of
the initial requests originates from a process with NONE (default) priority.
So we can get a situation when a process with default ioprio will experience
IO starvation, while there is no process from real-time class in the system.

Just removing ioprio_valid check should correct situation.

Signed-off-by: Vasily Tarasov <vtaras@openvz.org>

--

--- linux-2.6.18/fs/ioprio.c.orig 2006-09-20 07:42:06.000000000 +0400
+++ linux-2.6.18/fs/ioprio.c 2006-10-12 14:52:36.000000000 +0400
@@ -145,11 +145,6 @@ int ioprio_best(unsigned short aprio, un
unsigned short aclass = IOPRIO_PRIO_CLASS(aprio);
unsigned short bclass = IOPRIO_PRIO_CLASS(bprio);

- if (!ioprio_valid(aprio))
- return bprio;
- if (!ioprio_valid(bprio))
- return aprio;
-
if (aclass == IOPRIO_CLASS_NONE)
aclass = IOPRIO_CLASS_BE;
if (bclass == IOPRIO_CLASS_NONE)
-
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: 2006-10-12 14:15    [W:0.040 / U:0.436 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site