On Fri, Feb 08, 2019 at 07:13:39AM +0000, Alexey Brodkin wrote: > Hi Greg, > > > -----Original Message----- > > From: gre...@linuxfoundation.org <gre...@linuxfoundation.org> > > Sent: Thursday, February 7, 2019 6:52 PM > > To: Alexey Brodkin <alexey.brod...@synopsys.com> > > Cc: david.lai...@aculab.com; ge...@linux-m68k.org; pet...@infradead.org; > > sta...@vger.kernel.org; > > t...@linutronix.de; will.dea...@arm.com; Vineet Gupta > > <vineet.gup...@synopsys.com>; linux-snps- > > a...@lists.infradead.org > > Subject: Re: patch "devres: Align data[] to ARCH_KMALLOC_MINALIGN" added to > > driver-core-linus > > [snip] > > > Ah, I was waiting to see if you would notice :) > > Well I was just patiently waiting as I guess there's a long queue > of patches to deal with in your inbox :) > > > See this question from Linus about this patch: > > > > https://lore.kernel.org/lkml/CAHk-=wj3q7ckmqywfzssqutqkehnwvgrrbcwe7avj70s8i5...@mail.gmail.com/ > > I didn't see that. Though I intentionally sent my patch to most if not all > arch maintainers so they might share their concerns... but IIRC nobody ever > replied with either concerns or acks. > > Also I do agree that it's a trade-off between: > 1. Predictability > I was completely sure devm-allocated buffer is the same as anything > kmalloced > except some meta-data stored _separately_ and so supposed alignment > should match as well... but how wrong that feeling was. > > 2. Optimization > Indeed it's so sweet when both devm "meta-data" and real small buffer fit > into 1 cache line. > > > I figured that you all did this for a good reason, and wasting that much > > space was going to be ok. But, I wanted to be sure, so if you never > > noticed it, I figured it was not that pressing of an issue. > > It's not super pressing because: > 1. Fortunately [or unfortunately] this problem happens only in pretty rare > cases > like that Etnaviv driver where I first caught it. > > 2. There's a solution and affected parties may apply known patch locally. > > > Anyway, is this really needed to be backported? > > For us poor ARC developers and users it's really needed as our tools ABI > sets 32-bit alignment for 64-bit types. See that's the same optimization - > why wasting precious bytes on useless holes - let's pack data tighter :) > > So having that fix at least in the most recent LTS (i.e. 4.19) would be > really good. > As for older kernels I think for now we may not touch them as indeed change is > quite intrusive.
Ok, that sounds reasonable. I'll go add the patch there and see if the ARM64 people even notice :) thanks, greg k-h _______________________________________________ linux-snps-arc mailing list linux-snps-arc@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-snps-arc
