On 4 July 2017 at 21:55, De Lara Guarch, Pablo <pablo.de.lara.gua...@intel.com> wrote: > > >> -----Original Message----- >> From: Thomas Monjalon [mailto:tho...@monjalon.net] >> Sent: Tuesday, July 4, 2017 12:26 AM >> To: Dumitrescu, Cristian <cristian.dumitre...@intel.com>; De Lara Guarch, >> Pablo <pablo.de.lara.gua...@intel.com> >> Cc: dev@dpdk.org; Jianbo Liu <jianbo....@linaro.org>; >> jerin.ja...@caviumnetworks.com; ashwin.sek...@caviumnetworks.com >> Subject: Re: [dpdk-dev] [PATCH] examples/ip_pipeline: use crc32 in hash >> functions for arm64 >> >> 04/07/2017 01:19, Dumitrescu, Cristian: >> > From: Thomas Monjalon [mailto:tho...@monjalon.net] >> > > 18/05/2017 11:09, Jianbo Liu: >> > > > Implement the same hash functions with crc32 on arm platform. >> > > > >> > > > Signed-off-by: Jianbo Liu <jianbo....@linaro.org> >> > > > --- >> > > > examples/ip_pipeline/pipeline/hash_func.h | 2 + >> > > > examples/ip_pipeline/pipeline/hash_func_arm64.h | 245 >> > > ++++++++++++++++++++++++ >> > > > 2 files changed, 247 insertions(+) create mode 100644 >> > > > examples/ip_pipeline/pipeline/hash_func_arm64.h >> > > >> > > I don't understand why this code is in an example. >> > > We have some CRC code in librte_hash, librte_net and ip_pipeline. >> > > Cristian, Jianbo, >> > > does it make sense to move these functions somewhere else? >> > > >> > >> > I think example apps are a great way to propose new hash functions. >> > IMO we should encourage the definition/exploration of new hash >> functions in our example apps. >> > >> > These functions are examples of how fast hash functions can be built >> using special CPU instructions. >> > They have much better performance than e.g. jhash, but their >> > properties are largely unknown, as no rigorous study on their >> > properties (such as uniform distribution) has been conducted. I have >> > seen them providing good performance for the data set I have been >> using, but I have no extensive data to support their maturity level. >> > >> > If somebody is willing to invest the effort in proving them, I would >> > be more than happy to see them moved to a library like librte_hash. >> > Pablo as maintainer has the choice (I think it is not the first time >> > we discuss bout these hash funcs :) ) >> > >> > As mentioned in one of our deprecation notices, I am actively working >> > (not ready for 17.8 unfortunately) to add a key mask parameter to these >> functions, so more work on these hash functions is likely to take place. >> >> OK thanks for the explanation. >> I still think we do not need to prove hash for integrating them. >> I would be interested to read Pablo's opinion. > > If these functions are used as hash functions, I would place them in rte_hash. > > The case where we placed the CRC function in librte_net was because that > was not used as a hash function, so it made sense to me placing it there, > but in this case, it looks like it is, so I think rte_hash is a valid place > (although someone would need to integrate it with the existing CRC hash > function in that library). >
I think Cristian explanation justified using the special hash functions here. And they may have better performance than the standard functions in the library. Thanks! Jianbo
