From: "Xu, Ting" <ting.xu@intel.com> To: "Dumitrescu, Cristian" <cristian.dumitrescu@intel.com>, David Marchand <david.marchand@redhat.com> Cc: dev <dev@dpdk.org>, dpdk stable <stable@dpdk.org>, Kevin Traynor <ktraynor@redhat.com>, Luca Boccassi <bluca@debian.org> Subject: Re: [dpdk-stable] [dpdk-dev] [PATCH v4] lib/table: fix cache alignment issue Date: Thu, 30 Jul 2020 06:57:44 +0000 Message-ID: <CY4PR1101MB2310ACC3491D123779DC3E96F8710@CY4PR1101MB2310.namprd11.prod.outlook.com> (raw) In-Reply-To: <BYAPR11MB293542E4B50F98B59075F8ABEB700@BYAPR11MB2935.namprd11.prod.outlook.com> Hi, all, > -----Original Message----- > From: Dumitrescu, Cristian <cristian.dumitrescu@intel.com> > Sent: Wednesday, July 29, 2020 10:53 PM > To: David Marchand <david.marchand@redhat.com> > Cc: Xu, Ting <ting.xu@intel.com>; dev <dev@dpdk.org>; dpdk stable > <stable@dpdk.org>; Kevin Traynor <ktraynor@redhat.com>; Luca Boccassi > <bluca@debian.org> > Subject: RE: [dpdk-stable] [dpdk-dev] [PATCH v4] lib/table: fix cache alignment > issue > > > > > -----Original Message----- > > From: David Marchand <david.marchand@redhat.com> > > Sent: Wednesday, July 29, 2020 3:00 PM > > To: Dumitrescu, Cristian <cristian.dumitrescu@intel.com> > > Cc: Xu, Ting <ting.xu@intel.com>; dev <dev@dpdk.org>; dpdk stable > > <stable@dpdk.org>; Kevin Traynor <ktraynor@redhat.com>; Luca Boccassi > > <bluca@debian.org> > > Subject: Re: [dpdk-stable] [dpdk-dev] [PATCH v4] lib/table: fix cache > > alignment issue > > > > On Wed, Jul 29, 2020 at 3:54 PM Dumitrescu, Cristian > > <cristian.dumitrescu@intel.com> wrote: > > > > -----Original Message----- > > > > From: David Marchand <david.marchand@redhat.com> > > > > Sent: Wednesday, July 29, 2020 2:28 PM > > > > To: Dumitrescu, Cristian <cristian.dumitrescu@intel.com> > > > > Cc: Xu, Ting <ting.xu@intel.com>; dev <dev@dpdk.org>; dpdk stable > > > > <stable@dpdk.org>; Kevin Traynor <ktraynor@redhat.com>; Luca > > Boccassi > > > > <bluca@debian.org> > > > > Subject: Re: [dpdk-stable] [dpdk-dev] [PATCH v4] lib/table: fix > > > > cache alignment issue > > > > > > > > On Wed, Jul 29, 2020 at 3:14 PM Dumitrescu, Cristian > > > > <cristian.dumitrescu@intel.com> wrote: > > > > > > Please correct me if I am wrong, but it simply means this part > > > > > > of the table library never worked for 32-bit. > > > > > > It seems more adding 32-bit support rather than a fix and then > > > > > > I wonder if it has its place in rc3. > > > > > > > > > > > > > > > > Functionally. the code works, but performance is affected. > > > > > > > > > > The only thing that prevents the code from working is the check > > > > > in the > > > > table create function that checks the size of the above structure > > > > is 64 > > bytes, > > > > which caught this issue. > > > > > > > > Yes, and that's my point. > > > > It was not working. > > > > It was not tested. > > > > > > > > > > > > > > Not sure when this code was last tested on 32-bit systems, I'll let > > > the > > validation folks comment on this, but I cannot rule out a change in > > compiler behavior either. > > > > > > This is a low complexity and low impact change, hence low risk IMO. > > > > Risk is to be evaluated when there is a need. > > I got pinged on this, like it was the end of the times. > > > > Then I find something that is not worth looking at, hence I am a bit irritated. > > > > I got pinged as well, and I also had to allocate time on this patch. It probably > means it is important for somebody. > > > And please, for the 2nd time, can you look at my comment below? > > > Sorry, I missed it first. > > > > > > > > > > diff --git a/lib/librte_table/rte_table_hash_key16.c > > > > > > b/lib/librte_table/rte_table_hash_key16.c > > > > > > > index 2cca1c924..c4384b114 100644 > > > > > > > --- a/lib/librte_table/rte_table_hash_key16.c > > > > > > > +++ b/lib/librte_table/rte_table_hash_key16.c > > > > > > > @@ -33,6 +33,7 @@ > > > > > > > > > > > > > > #endif > > > > > > > > > > > > > > +#ifdef RTE_ARCH_64 > > > > > > > struct rte_bucket_4_16 { > > > > > > > /* Cache line 0 */ > > > > > > > uint64_t signature[4 + 1]; @@ -46,6 +47,22 @@ struct > > > > > > > rte_bucket_4_16 { > > > > > > > /* Cache line 2 */ > > > > > > > uint8_t data[0]; > > > > > > > }; > > > > > > > +#else > > > > > > > +struct rte_bucket_4_16 { > > > > > > > + /* Cache line 0 */ > > > > > > > + uint64_t signature[4 + 1]; > > > > > > > + uint64_t lru_list; > > > > > > > + struct rte_bucket_4_16 *next; > > > > > > > + uint32_t pad; > > > > > > > + uint64_t next_valid; > > > > > > > + > > > > > > > + /* Cache line 1 */ > > > > > > > + uint64_t key[4][2]; > > > > > > > + > > > > > > > + /* Cache line 2 */ > > > > > > > + uint8_t data[0]; > > > > > > > +}; > > > > > > > +#endif > > > > > > > > > > > > The change could simply be: > > > > > > > > > > > > @@ -38,6 +38,9 @@ struct rte_bucket_4_16 { > > > > > > uint64_t signature[4 + 1]; > > > > > > uint64_t lru_list; > > > > > > struct rte_bucket_4_16 *next; > > > > > > +#ifndef RTE_ARCH_64 > > > > > > + uint32_t pad; > > > > > > +#endif > > > > > > uint64_t next_valid; > > > > > > > > > > > > /* Cache line 1 */ > > > > > > > > > > > > It avoids duplicating the whole structure definition (we could > > > > > > miss updating one side of the #ifdef later). > > > > > > Idem for the other "8" and "32" structures. > > > > > > > > > > > > What about this comment? > > > > What about this comment? > > > > You might suspect I also thought about this option. My preference is for the > option in the patch for the reasons that IMO it is easier to read and > understand the reason for the difference, even though the code is slightly > larger. It also leaves the 64-bit code untouched, so it is easier to remove when > we finally decide at some point to drop the 32-bit support. > > But I can live with the option you describe as well. Thanks for the input. > > For me, it would be great if somebody on this list could indicate why the 4- > byte padding was not inserted by the compiler automatically, and hence the > need for this fix. > Thanks for your help and additional works on this patch. The validation team tested this case in a 32-bit environment, besides, there are a series of similar tests in 32-bit environment as well. There might be some practical needs for this. Therefore, before we decide to drop 32-bit support formally, I think such modification is OK, if we cannot fix the compiler issue directly. Shall I update the patch as David suggested to make it simpler? > > > > -- > > David Marchand
next prev parent reply other threads:[~2020-07-30 6:57 UTC|newest] Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-06-16 16:27 [dpdk-stable] [PATCH v1] " Ting Xu 2020-06-17 5:43 ` [dpdk-stable] [PATCH v2] " Ting Xu 2020-07-02 8:06 ` [dpdk-stable] [dpdk-dev] " Zhou, JunX W 2020-07-09 1:48 ` [dpdk-stable] [PATCH v3] " Ting Xu 2020-07-20 14:37 ` Dumitrescu, Cristian 2020-07-21 5:15 ` Xu, Ting 2020-07-21 21:16 ` Dumitrescu, Cristian 2020-07-22 2:16 ` Xu, Ting 2020-07-22 2:16 ` [dpdk-stable] [PATCH v4] " Ting Xu 2020-07-22 8:26 ` Dumitrescu, Cristian 2020-07-22 8:30 ` Xu, Ting 2020-07-22 8:49 ` Dumitrescu, Cristian 2020-07-22 8:48 ` Dumitrescu, Cristian 2020-07-29 12:01 ` [dpdk-stable] [dpdk-dev] " David Marchand 2020-07-29 13:13 ` Dumitrescu, Cristian 2020-07-29 13:28 ` David Marchand 2020-07-29 13:54 ` Dumitrescu, Cristian 2020-07-29 13:59 ` David Marchand 2020-07-29 14:53 ` Dumitrescu, Cristian 2020-07-30 6:57 ` Xu, Ting [this message] 2020-07-30 10:35 ` Kevin Traynor 2020-09-09 6:18 ` Xu, Ting 2020-09-15 8:03 ` David Marchand 2020-10-14 8:26 ` Xu, Ting 2020-10-14 13:53 ` David Marchand
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