On Fri, 29 Aug 2014 13:44:31 -0700 Mike Travis <travis@xxxxxxx> wrote: > > > On 8/29/2014 1:16 PM, Andrew Morton wrote: > > On Fri, 29 Aug 2014 14:53:28 -0500 Mike Travis <travis@xxxxxxx> wrote: > > > >> > >> We have a large university system in the UK that is experiencing > >> very long delays modprobing the driver for a specific I/O device. > >> The delay is from 8-10 minutes per device and there are 31 devices > >> in the system. This 4 to 5 hour delay in starting up those I/O > >> devices is very much a burden on the customer. > >> > >> There are two causes for requiring a restart/reload of the drivers. > >> First is periodic preventive maintenance (PM) and the second is if > >> any of the devices experience a fatal error. Both of these trigger > >> this excessively long delay in bringing the system back up to full > >> capability. > >> > >> The problem was tracked down to a very slow IOREMAP operation and > >> the excessively long ioresource lookup to insure that the user is > >> not attempting to ioremap RAM. These patches provide a speed up > >> to that function. > >> > > > > Really would prefer to have some quantitative testing results in here, > > as that is the entire point of the patchset. And it leaves the reader > > wondering "how much of this severe problem remains?". > > Okay, I have some results from testing. The modprobe time appears to > be affected quite a bit by previous activity on the ioresource list, > which I suspect is due to cache preloading. While the overall > improvement is impacted by other overhead of starting the devices, > this drastically improves the modprobe time. > > Also our system is considerably smaller so the percentages gained > will not be the same. Best case improvement with the modprobe > on our 20 device smallish system was from 'real 5m51.913s' to > 'real 0m18.275s'. Thanks, I slurped that into the changelog. > > Also, the -stable backport is a big ask, isn't it? It's arguably > > notabug and the affected number of machines is small. > > > > Ingo had suggested this. We are definitely pushing it to our distro > suppliers for our customers. Whether it's a big deal for smaller > systems is up in the air. Note that the customer system has 31 devices > on an SSI that includes a large number of other IB and SAS devices > as well as a number of nodes which all which have discontiguous memory > segments. I'm envisioning an ioresource list that numbers at least > several hundred entries. While that's somewhat indicative of typical > UV systems it is generally not that common otherwise. > > So I guess the -stable is merely a suggestion, not a request. Cc Greg for his thoughts! -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>