linux-mips
[Top] [All Lists]

Re: tasklet latency and system calls on mips

To: Jun Sun <jsun@mvista.com>
Subject: Re: tasklet latency and system calls on mips
From: "Sirotkin, Alexander" <demiurg@ti.com>
Date: Mon, 18 Aug 2003 18:29:52 +0300
Cc: linux-mips@linux-mips.org
In-reply-to: <20030814094515.B1203@mvista.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <3F3A411C.70603@ti.com> <20030813095446.C9655@mvista.com> <3F3B53C0.30408@ti.com> <20030814094515.B1203@mvista.com>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.4) Gecko/20030624 Netscape/7.1


Jun Sun wrote:
On Thu, Aug 14, 2003 at 12:17:52PM +0300, Sirotkin, Alexander wrote:
  
I suspect that what happens is as follows :

system call arrives and while it's being processed and interrupt to one
of the drivers arrives. This interrupt 
schedules a tasklet which however is not executed after the system call
finishes, 
    
The tasklet should be executed at the return of interrupt handling.
If not, there is a bug.
  
I have a feeling that we are going in circles. Tasklets are executed at the return of interrupt handler.
However, I suspect that this is not enough. On mips (contrary to x86), system call is NOT an interrupt.
It's a different exception with different handler. Therefore I suspect that tasklets are NOT called at
the end of system call exception handler (which is a different handler, not do_IRQ).

  
only after the next timer
interrupt which causes up to 10 ms latency (not all the time, only when
somebody makes a system call).

    
BTW, make sure tasklet_schedule() is indeed called in an interrupt handler.
I am not sure why will happen otherwise.

If you suspect it is a bug, you can easily trace them.  You may my
little tracing tool useful,
I can try to trace it, I just wanted to ensure that what I was saying makes sense. See above.

	http://linux.junsun.net/patches/generic/experimental/030716.a-jstrace.patch

Jun
  

-- 
Alexander Sirotkin
SW Engineer

Texas Instruments
Broadband Communications Israel (BCIL)
Tel:  +972-9-9706587
________________________________________________________________________
"Those who do not understand Unix are condemned to reinvent it, poorly."
      -- Henry Spencer 
<Prev in Thread] Current Thread [Next in Thread>