diff mbox

[2/2] pkt_sched: Change PSCHED_SHIFT from 10 to 6

Message ID 20090609080513.GB5237@ff.dom.local
State Accepted, archived
Delegated to: David Miller
Headers show

Commit Message

Jarek Poplawski June 9, 2009, 8:05 a.m. UTC
Change PSCHED_SHIFT from 10 to 6 to increase schedulers time
resolution. This will increase 16x a number of (internal) ticks per
nanosecond, and is needed to improve accuracy of schedulers based on
rate tables, like HTB, TBF or CBQ, with rates above 100Mbit. It is
assumed this change is safe for 32bit accounting of time diffs up
to 2 minutes, which should be enough for common use (extremely low
rate values may overflow, so get inaccurate instead). To make full
use of this change an updated iproute2 will be needed. (But using
older iproute2 should be safe too.)

This change breaks ticks - microseconds similarity, so some minor code
fixes might be needed. It is also planned to change naming adequately
eg. to PSCHED_TICKS2NS() etc. in the near future.

Reported-by: Antonio Almeida <vexwek@gmail.com>
Tested-by: Antonio Almeida <vexwek@gmail.com>
Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
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Comments

David Miller June 9, 2009, 12:21 p.m. UTC | #1
From: Jarek Poplawski <jarkao2@gmail.com>
Date: Tue, 9 Jun 2009 08:05:13 +0000

> Change PSCHED_SHIFT from 10 to 6 to increase schedulers time
> resolution. This will increase 16x a number of (internal) ticks per
> nanosecond, and is needed to improve accuracy of schedulers based on
> rate tables, like HTB, TBF or CBQ, with rates above 100Mbit. It is
> assumed this change is safe for 32bit accounting of time diffs up
> to 2 minutes, which should be enough for common use (extremely low
> rate values may overflow, so get inaccurate instead). To make full
> use of this change an updated iproute2 will be needed. (But using
> older iproute2 should be safe too.)
> 
> This change breaks ticks - microseconds similarity, so some minor code
> fixes might be needed. It is also planned to change naming adequately
> eg. to PSCHED_TICKS2NS() etc. in the near future.
> 
> Reported-by: Antonio Almeida <vexwek@gmail.com>
> Tested-by: Antonio Almeida <vexwek@gmail.com>
> Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>

Applied.
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diff mbox

Patch

diff -Nurp a/include/net/pkt_sched.h b/include/net/pkt_sched.h
--- a/include/net/pkt_sched.h	2009-06-08 23:06:31.000000000 +0200
+++ b/include/net/pkt_sched.h	2009-06-08 23:23:53.000000000 +0200
@@ -41,8 +41,8 @@  static inline void *qdisc_priv(struct Qd
 typedef u64	psched_time_t;
 typedef long	psched_tdiff_t;
 
-/* Avoid doing 64 bit divide by 1000 */
-#define PSCHED_SHIFT			10
+/* Avoid doing 64 bit divide */
+#define PSCHED_SHIFT			6
 #define PSCHED_US2NS(x)			((s64)(x) << PSCHED_SHIFT)
 #define PSCHED_NS2US(x)			((x) >> PSCHED_SHIFT)