lkml.org 
[lkml]   [1999]   [May]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: Overscheduling DOES happen with high web server load.
Date
In muc.lists.linux-kernel, you wrote:
>> Ok, you are right. The real problem is we are calculating goodness
>> O(A*B).
>>
>> A= Number of processes on the runqueue
>> B= Number of times schedule is called
>
>This is the amount of work we are doing, but I think you're on to the
>wrong solution. Phil did a test: he patched schedule() to pick the
>first schedulable process instead of the best one. That dropped the
>amount of time consumed in schedule() from 20% to 1%. That's the same
>as reducing the work from O(A*B) to O(B).
>
>Why is schedule called so frequently? The thundering herd. You get a
>new connection, everyone wakes up, only one gets work, and everyone
>else goes back to sleep, each causing O(A) work to reschedule. M hits
>per second, N processes, B=M*N. A=N. So the total work is O(M*N^2).

It was shown earlier in the thread that no thundering herd occured in the test,
because apache serializes the accept with a lock.

-Andi

-
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 13:51    [W:0.126 / U:2.428 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site