lkml.org 
[lkml]   [2009]   [Dec]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: problems in linux-next (Was: Re: linux-next: Tree for December 1)
Hello,

On 12/02/2009 01:01 AM, Ingo Molnar wrote:
>>> The problem is that on UP configurations. Percpu memory allocator
>>> becomes a simple wrapper around kmalloc and there's no way to
>>> specify larger alignment when requesting memory from kmalloc.
>>
>> There is usually no point in aligning in UP. Alignment is typically
>> done for smp configurations to limit cache line bouncing and control
>> cache line use/
>
> There is a natural minimum alignment for UP and it's smaller than the
> cache-line size: machine word size. All our allocators (except bootmem)
> align to machine word so there's no need to specify this explicitly.
>
> Larger alignment than that just wastes memory - which waste UP systems
> can afford the least.

This isn't usual alignment. struct work_struct has one data fields
which is overloaded for two purposes. Lower few bits are used to
carry flags while upper bits are used to point to sruct
cpu_workqueue_struct. So, the number of available bits for flags are
determined by the alignment of cpu_workqueue_struct. Memory usage for
cwqs isn't a big concern here. Many workqueues will go away. I think
we'll end up with less than half of what we have today while we'll
continue to have large number of works.

I'll just create alloc_cwq function which forces the alignment on UP.

Thanks.

--
tejun


\
 
 \ /
  Last update: 2009-12-02 00:25    [W:0.069 / U:0.068 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site