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Date: Tue, 18 Nov 2014 14:47:15 -0800 From: Alexander Duyck <alexander.h.duyck@...hat.com> To: Linus Torvalds <torvalds@...ux-foundation.org> CC: "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>, Network Development <netdev@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>, Peter Zijlstra <peterz@...radead.org>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Heiko Carstens <heiko.carstens@...ibm.com>, Ingo Molnar <mingo@...nel.org>, Michael Neuling <mikey@...ling.org>, Russell King - ARM Linux <linux@....linux.org.uk>, donald.c.skidmore@...el.com, matthew.vick@...el.com, Geert Uytterhoeven <geert@...ux-m68k.org>, Jeff Kirsher <jeffrey.t.kirsher@...el.com>, Francois Romieu <romieu@...zoreil.com>, Paul McKenney <paulmck@...ux.vnet.ibm.com>, nic_swsd@...ltek.com, Will Deacon <will.deacon@....com>, Michael Ellerman <michael@...erman.id.au>, Tony Luck <tony.luck@...el.com>, Oleg Nesterov <oleg@...hat.com>, Martin Schwidefsky <schwidefsky@...ibm.com>, Frédéric Weisbecker <fweisbec@...il.com>, David Miller <davem@...emloft.net> Subject: Re: [PATCH v4 0/4] Add lightweight memory barriers for coherent memory access On 11/18/2014 12:53 PM, Linus Torvalds wrote: > On Tue, Nov 18, 2014 at 9:28 AM, Alexander Duyck > <alexander.h.duyck@...hat.com> wrote: >> These patches introduce two new primitives for synchronizing cache coherent >> memory writes and reads. These two new primitives are: >> >> coherent_rmb() >> coherent_wmb() > > So I'm still not convinced about the name. I don't hate it, but if you > ever want to do "read_acquire", then that whole "coherent_" thing does > make for a big mouthful. I don't see why "dma" isn't simpler and more > to the point, and has the advantage of lining up (in documentation > etc) with "smp". The problem is DMA is a broad brush. There are multiple cases I can think of where DMA does not represent coherent memory. > Why would you ever use "coherent_xyz()" on something that isn't about > dma? If it's cache-coherent memory without DMA, you'd use "smp_xyz()", > so I really do prefer that whole "dma-vs-smp" issue, because it talks > about what is actually the important issue. All sane memory is > coherent, after all (and if it isn't, you have other issues than > memory ordering). > > Linus This barrier only applies to a subset of DMA memory types. So yes, "coherent_xyz()" only applies to DMA, but not all DMA memory is coherent as it could be a non-coherent or streaming DMA mapping. One spot where the name makes sense is in the headers themselves. To avoid duplication of definitions in several spots if CONFIG_SMP was defined I simply defined smp_xyz() as coherent_xyz(). Defining it as dma_xyz() might have made that more difficult to read in terms of what was going on. - Alex -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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