RE: [Linux-nvdimm] [PATCH v2 19/20] nd_btt: atomic sector updates

[Elliott, Robert (Server Storage)]

> -----Original Message-----
> From: dan.j.williams@xxxxxxxxx [mailto:dan.j.williams@xxxxxxxxx] On
> Behalf Of Dan Williams
> Sent: Saturday, May 16, 2015 10:22 PM
> To: Elliott, Robert (Server Storage)
> Cc: linux-nvdimm@xxxxxxxxxxxx; Neil Brown; Greg KH; Dave Chinner; linux-
> kernel@xxxxxxxxxxxxxxx; Andy Lutomirski; Jens Axboe; H. Peter Anvin;
> Christoph Hellwig; Ingo Molnar
> Subject: Re: [Linux-nvdimm] [PATCH v2 19/20] nd_btt: atomic sector
> updates
> 
> On Sat, May 16, 2015 at 6:19 PM, Elliott, Robert (Server Storage)
> <Elliott@xxxxxx> wrote:
> >
...
> 2 items to check:
> 
> 1/ make sure you have a your btt sector size set to 4k which cuts down
> the overhead by a factor of 8.
> 
> 2/ boot with nr_cpus=256 or lower.
> 
> Ross noticed that CONFIG_NR_CPUS is set quite high on distro kernels
> which revealed that we should have been using nr_cpu_ids and percpu
> variables for nd_region_acquire_lane() from the outset.  This fix is
> coming in v3.

My system does have CONFIG_NR_CPUS=8192.  I'll try the items you 
suggested.