On Tue, 2018-03-27 at 10:46 -0400, Sinan Kaya wrote: > combined buffers. > > Alex: > "Don't bother. I can tell you right now that for x86 you have to have a > wmb() before the writel().
No, this isn't the semantics of writel. You shouldn't need it unless something changed and we need to revisit our complete understanding of *all* MMIO accessor semantics. At least for UC space, it has always been accepted (and enforced) that writel would not require any other barrier to order vs. previous stores to memory. > Based on the comment in > (https://www.spinics.net/lists/linux-rdma/msg62666.html): > Replacing wmb() + writel() with wmb() + writel_relaxed() will work on > PPC, it will just not give you a benefit today. > > I say the patch set stays. This gives benefit on ARM, and has no > effect on x86 and PowerPC. If you want to look at trying to optimize > things further on PowerPC and such then go for it in terms of trying > to implement the writel_relaxed(). Otherwise I say we call the ARM > goodness a win and don't get ourselves too wrapped up in trying to fix > this for all architectures."