On Wed, 2015-04-22 at 10:17 -0600, Jason Gunthorpe wrote: > On Wed, Apr 22, 2015 at 05:23:28PM +0200, Luis R. Rodriguez wrote: > > On Tue, Apr 21, 2015 at 11:39:39PM -0600, Jason Gunthorpe wrote: > > > On Wed, Apr 22, 2015 at 01:39:07AM +0200, Luis R. Rodriguez wrote: > > > > > Mike, do you think the time is right to just remove the iPath driver? > > > > > > > > With PAT now being default the driver effectively won't work > > > > with write-combining on modern kernels. Even if systems are old > > > > they likely had PAT support, when upgrading kernels PAT will work > > > > but write-combing won't on ipath. > > > > > > Sorry, do you mean the driver already doesn't get WC? Or do you mean > > > after some more pending patches are applied? > > > > No, you have to consider the system used and the effects of calls used > > on the driver in light of this table: > > So, just to be clear: > > At some point Linux started setting the PAT bits during > ioremap_nocache, which overrides MTRR, and at that point the driver > became broken on all PAT capable systems? > > Not only that, but we've only just noticed it now, and no user ever > complained? > > So that means either no users exist, or all users are on non-PAT > systems? > > This driver only works on x86-64 systems. Are there any x86-64 systems > that are not PAT capable? IIRC even the first Opteron had PAT, but my > memory is fuzzy from back then :| > > > Another option in order to enable this type of checks at run time > > and still be able to build the driver on standard distributions and > > just prevent if from loading on PAT systems is to have some code in > > place which would prevent the driver from loading if PAT was > > enabled, this would enable folks to disable PAT via a kernel command > > line option, and if that was used then the driver probe would > > complete. > > This seems like a reasonble option to me. At the very least we might > learn if anyone is still using these cards. > > I'd also love to remove the driver if it turns out there are actually > no users. qib substantially replaces it except for a few very old > cards. To be precise, the split is that ipath powers the old HTX bus cards that only work in AMD systems, qib is all PCI-e cards. I still have a few HTX cards, but I no longer have any systems with HTX slots, so we haven't even used this driver in testing for 3 or 4 years now. And these are all old SDR cards, where the performance numbers were 800MB/s with WC enabled, 50MB/s without it. > Mike? > > Jason > -- > To unsubscribe from this list: send the line "unsubscribe linux-rdma" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Doug Ledford <dledford@xxxxxxxxxx> GPG KeyID: 0E572FDD
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