> -----Original Message----- > From: Neil Horman [mailto:nhorman at tuxdriver.com] > Sent: Wednesday, August 06, 2014 1:19 PM > To: Ananyev, Konstantin > Cc: dev at dpdk.org; Thomas Monjalon; Richardson, Bruce > Subject: Re: [PATCH] acl: If build does not support sse4.2, emulate missing > instructions with C code > > On Wed, Aug 06, 2014 at 11:39:22AM +0000, Ananyev, Konstantin wrote: > > > > > > > -----Original Message----- > > > From: Neil Horman [mailto:nhorman at tuxdriver.com] > > > Sent: Tuesday, August 05, 2014 7:21 PM > > > To: Ananyev, Konstantin > > > Cc: dev at dpdk.org; Thomas Monjalon; Richardson, Bruce > > > Subject: Re: [PATCH] acl: If build does not support sse4.2, emulate > > > missing instructions with C code > > > > > > On Tue, Aug 05, 2014 at 03:26:27PM +0000, Ananyev, Konstantin wrote: > > > > Hi Neil, > > > > > > > > > From: Neil Horman [mailto:nhorman at tuxdriver.com] > > > > > Sent: Monday, August 04, 2014 4:36 PM > > > > > To: dev at dpdk.org > > > > > Cc: Neil Horman; Thomas Monjalon; Ananyev, Konstantin; Richardson, > > > > > Bruce > > > > > Subject: [PATCH] acl: If build does not support sse4.2, emulate > > > > > missing instructions with C code > > > > > > > > > > The ACL library makes extensive use of some SSE4.2 instructions, > > > > > which means the > > > > > default build can't compile this library. Work around the problem by > > > > > testing > > > > > the __SSE42__ definition in the acl_vects.h file and defining the > > > > > macros there > > > > > as intrinsics or c-level equivalants. Note this is a minimal patch, > > > > > adjusting > > > > > only the definitions that are currently used in the ACL library. > > > > > > > > > > > > > My comments about actual implementations of c-level equivalents below. > > > > None of them look correct to me. > > > > Of course it could be fixed. > > > > Though I am not sure that is a right way to proceed: > > > > At first I really doubt that these equivalents will provide similar > > > > performance. > > > > As you probably note - we do have a scalar version of > > > > rte_acl_classify(): rte_acl_classify_scalar(). > > > > So I think it might be faster than vector one with 'emulated' > > > > instrincts. > > > > Unfortunately it is all mixed right now into one file and 'scalar' > > > > version could use few sse4 instrincts through resolve_priority(). > > > > Another thing - we consider to add another version of > > > > rte_acl_classify() that will use avx2 instrincts. > > > > If we go the way you suggest - I am afraid will soon have to provide > > > > scalar equivalents for several AVX2 instrincts too. > > > > So in summary that way (providing our own scalar equivalents of SIMD > > > > instrincts) seems to me slow, hard to maintain and error > > > prone. > > > > > > > > What porbably can be done instead: rework acl_run.c a bit, so it > > > > provide: > > > > rte_acl_classify_scalar() - could be build and used on all systems. > > > > rte_acl_classify_sse() - could be build and used only on systems with > > > > sse4.2 and upper, return ENOTSUP on lower arch. > > > > In future: rte_acl_classify_avx2 - could be build and used only on > > > > systems with avx2 and upper, return ENOTSUP on lower arch. > > > > > > > > I am looking at rte_acl right now anyway. > > > > So will try to come up with something workable. > > > > > > > So, this is exactly the opposite of what Bruce and I just spent several > > > days and > > > a huge email thread that you clearly are aware of discussing run time > > > versus > > > compile time selection of paths. At this point I'm done ping ponging > > > between > > > your opposing viewpoints. If you want to implement something that does > > > run time > > > checking, I'm fine with it, but I'm not going back and forth until you > > > two come > > > to an agreement on this. > > > > Right now, I am not talking about 'run time vs compile time selection'. > But you are talking about exactly that, allbeit implicitly. To implement what > you recommend above (that being multiple functional paths that return a not > supported error code at run time), we need to make run time tests for what the > cpu supports. While I'm actually ok with doing that (I think it makes alot of > sense), Bruce and I just spent several days and dozens of emails debating > that, > so you can understand why I don't want to write yet another version of this > patch that requires doing the exact thing we just argued about, especially if > it > means he's going to pipe back up and say no, driving me back to a common > single > implementation that compiles and runs for all platforms. I'm not going to > keep > re-writing this boucing back and forth between your opposing viewpoints. We > need to agree on a direction before I make another pass at this. > > > Whatever way we choose, I think the implementation need to be: > > 1) correct > Obviously. > > > 2) allow easily add(/modify) code path optimised for particular > > architecture. > > Without need to modify/re-test what you call 'least common denominator' > > code path. > > And visa-versa, if someone find a way to optimise common code path - no > > need to > > touch/retest architecture specific ones. > So I'm fine with this, but it is anathema to what Bruce advocated for when I > did > this latest iteration. Bruce advocated for a single common path that compiled > in all cases. Bruce, do you want to comment here? I'd really like to get > this > settled before I go try this again. > > Neil >
Ok, let me try to prepare a patch with what I suggested. Hopefully it will make everyone reasonably happy. Konstantin
