lkml.org 
[lkml]   [2013]   [Aug]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC][PATCH] drivers: base: dynamic memory block creation
On Wed, Aug 14, 2013 at 01:35:46PM -0700, Greg Kroah-Hartman wrote:
> On Wed, Aug 14, 2013 at 01:05:33PM -0700, Dave Hansen wrote:
> > On 08/14/2013 12:43 PM, Greg Kroah-Hartman wrote:
> > > On Wed, Aug 14, 2013 at 02:31:45PM -0500, Seth Jennings wrote:
> > >> ppc64 has a normal memory block size of 256M (however sometimes as low
> > >> as 16M depending on the system LMB size), and (I think) x86 is 128M. With
> > >> 1TB of RAM and a 256M block size, that's 4k memory blocks with 20 sysfs
> > >> entries per block that's around 80k items that need be created at boot
> > >> time in sysfs. Some systems go up to 16TB where the issue is even more
> > >> severe.
> > >
> > > The x86 developers are working with larger memory sizes and they haven't
> > > seen the problem in this area, for them it's in other places, as I
> > > referred to in my other email.
> >
> > The SGI guys don't run normal distro kernels and don't turn on memory
> > hotplug, so they don't see this. I do the same in my testing of
> > large-memory x86 systems to speed up my boots. I'll go stick it back in
> > there and see if I can generate some numbers for a 1TB machine.
> >
> > But, the problem on x86 is at _worst_ 1/8 of the problem on ppc64 since
> > the SECTION_SIZE is so 8x bigger by default.
> >
> > Also, the cost of creating sections on ppc is *MUCH* higher than x86
> > when amortized across the number of pages that you're initializing. A
> > section on ppc64 has to be created for each (2^24/2^16)=256 pages while
> > one on x86 is created for each (2^27/2^12)=32768 pages.
> >
> > Thus, x86 folks with our small pages and large sections tend to be
> > focused on per-page costs. The ppc folks with their small sections and
> > larger pages tend to be focused on the per-section costs.
>
> Ah, thanks for the explaination, now it makes more sense why they are
> both optimizing in different places.

Yes, thanks Dave for explaining that for me :)

>
> But a "cleanup" patch first, and then the "change the logic to go
> faster" would be better here, so that we can review what is really
> happening.

Will do.

>
> thanks,
>
> greg k-h
>



\
 
 \ /
  Last update: 2013-08-14 23:41    [W:1.576 / U:1.572 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site