lkml.org 
[lkml]   [1999]   [Dec]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[patch] Re: setitimer lowlatency-2.2.13-A1 questions

On Mon, 6 Dec 1999, William Montgomery wrote:

> The following ktrace shows the behavior I describe:

oh, ok, i now know what the problem is:

> 120795.36 6.18 timer_interrupt pid(6801)

(bh gets marked, ok.)

> 120801.55 0.59 do_timer pid(6801)
> 120802.14 0.94 enable_8259A_irq pid(6801)
> 120803.08 0.14 do_IRQ pid(6801)
> 120803.22 0.16 do_bottom_half pid(6801)
> ^^^---- seems like timer_bh should run right after this

(but the networking code has disabled TIMER_BH so it doesnt get run!)

> 120803.38 2.53 do_IRQ pid(6801)
> 120805.91 2.31 kmem_cache_free pid(6801)
> 120808.22 0.87 del_timer pid(6801)

> 120811.79 2079.30 do_IRQ pid(6801)
> ^^^-- I think pid(6801) is running now *prior* to timer_bh

(networking code enables TIMER_BH, but it doesnt run it!)

> 122891.09 0.53 system_call pid(6801)
> 122891.62 0.81 sys_sigsuspend pid(6801)
> 122892.44 0.59 schedule pid(6801)
> 122893.03 0.30 do_bottom_half pid(6801)
> 122893.33 0.89 timer_bh pid(6801)

the next 'return to user-mode' (or interrupt) naturally runs the BH, but
belatedly.

the solution is to call do_bottom_half() in enable_bh():

if (active & mask)
do_bottom_half();

(see the attached patch - i have not even compiled it so beware.)

does this help?

-- mingo

--- linux/include/asm-i386/softirq.h.orig Mon Dec 6 19:27:28 1999
+++ linux/include/asm-i386/softirq.h Mon Dec 6 19:27:58 1999
@@ -136,6 +136,8 @@
if (atomic_dec_and_test(&bh_mask_count[nr]))
bh_mask |= 1 << nr;
spin_unlock_irqrestore(&i386_bh_lock, flags);
+ if (bh_mask & bh_active)
+ do_bottom_half();
}

#endif /* __ASM_SOFTIRQ_H */

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

\
 
 \ /
  Last update: 2005-03-22 13:55    [W:0.060 / U:0.088 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site