From: "Wang, Yipeng1" <yipeng1.wang@intel.com>
To: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
"Van Haaren, Harry" <harry.van.haaren@intel.com>,
"Richardson, Bruce" <bruce.richardson@intel.com>
Cc: "De Lara Guarch, Pablo" <pablo.de.lara.guarch@intel.com>,
"dev@dpdk.org" <dev@dpdk.org>,
"Gavin Hu (Arm Technology China)" <Gavin.Hu@arm.com>,
"Steve Capper" <Steve.Capper@arm.com>,
Ola Liljedahl <Ola.Liljedahl@arm.com>, nd <nd@arm.com>,
"Gobriel, Sameh" <sameh.gobriel@intel.com>
Subject: Re: [dpdk-dev] [PATCH 3/4] hash: fix rw concurrency while moving keys
Date: Thu, 4 Oct 2018 19:16:17 +0000 [thread overview]
Message-ID: <D2C4A16CA39F7F4E8E384D204491D7A6614EC098@FMSMSX151.amr.corp.intel.com> (raw)
In-Reply-To: <AM6PR08MB3672C8E2CC634B6BC95509BD98EA0@AM6PR08MB3672.eurprd08.prod.outlook.com>
>-----Original Message-----
>From: Honnappa Nagarahalli [mailto:Honnappa.Nagarahalli@arm.com]
>Sent: Wednesday, October 3, 2018 8:54 PM
>To: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>; Wang, Yipeng1 <yipeng1.wang@intel.com>; Van Haaren, Harry
><harry.van.haaren@intel.com>; Richardson, Bruce <bruce.richardson@intel.com>
>Cc: De Lara Guarch, Pablo <pablo.de.lara.guarch@intel.com>; dev@dpdk.org; Gavin Hu (Arm Technology China)
><Gavin.Hu@arm.com>; Steve Capper <Steve.Capper@arm.com>; Ola Liljedahl <Ola.Liljedahl@arm.com>; nd <nd@arm.com>; Gobriel,
>Sameh <sameh.gobriel@intel.com>
>Subject: RE: [dpdk-dev] [PATCH 3/4] hash: fix rw concurrency while moving keys
>
>>
>> > >-----Original Message-----
>> > >From: Van Haaren, Harry
>> > >> > > > > /**
>> > >> > > > > * Add a key to an existing hash table.
>> > >> > > > >@@ -222,7 +222,7 @@ rte_hash_add_key(const struct rte_hash
>> > >> > > > >*h, const void
>> > >> > > *key);
>> > >> > > > > * array of user data. This value is unique for this key.
>> > >> > > > > */
>> > >> > > > > int32_t
>> > >> > > > >-rte_hash_add_key_with_hash(const struct rte_hash *h, const
>> > >> > > > >void *key,
>> > >> > > hash_sig_t sig);
>> > >> > > > >+rte_hash_add_key_with_hash(struct rte_hash *h, const void
>> > >> > > > >+*key,
>> > >> > > hash_sig_t sig);
>> > >> > > > >
>> > >> > > > > /
>> > >> > > >
>> > >> > > > I think the above changes will break ABI by changing the
>> > >> > > > parameter
>> > >> type?
>> > >> > > Other people may know better on this.
>> > >> > >
>> > >> > > Just removing a const should not change the ABI, I believe,
>> > >> > > since the const is just advisory hint to the compiler. Actual
>> > >> > > parameter size and count remains unchanged so I don't believe there
>> is an issue.
>> > >> > > [ABI experts, please correct me if I'm wrong on this]
>> > >> >
>> > >> >
>> > >> > [Certainly no ABI expert, but...]
>> > >> >
>> > >> > I think this is an API break, not ABI break.
>> > >> >
>> > >> > Given application code as follows, it will fail to compile - even
>> > >> > though
>> > >> running
>> > >> > the new code as a .so wouldn't cause any issues (AFAIK).
>> > >> >
>> > >> > void do_hash_stuff(const struct rte_hash *h, ...) {
>> > >> > /* parameter passed in is const, but updated function
>> > >> > prototype is
>> > >> non-
>> > >> > const */
>> > >> > rte_hash_add_key_with_hash(h, ...); }
>> > >> >
>> > >> > This means that we can't recompile apps against latest patch
>> > >> > without application code changes, if the app was passing a const
>> > >> > rte_hash struct
>> > >> as
>> > >> > the first parameter.
>> > >> >
>> > >> Agree. Do we need to do anything for this?
>> > >
>> > >I think we should try to avoid breaking API wherever possible.
>> > >If we must, then I suppose we could follow the ABI process of a
>> > >deprecation notice.
>> > >
>> > >From my reading of the versioning docs, it doesn't document this case:
>> > >https://doc.dpdk.org/guides/contributing/versioning.html
>> > >
>> > >I don't recall a similar situation in DPDK previously - so I suggest
>> > >you ask Tech board for input here.
>> > >
>> > >Hope that helps! -Harry
>> > [Wang, Yipeng]
>> > Honnappa, how about use a pointer to the counter in the rte_hash
>> > struct instead of the counter? Will this avoid API change?
>> I think it defeats the purpose of 'const' parameter to the API and provides
>> incorrect information to the user.
>Yipeng, I think I have misunderstood your comment. I believe you meant; we could allocate memory to the counter and store the
>pointer in the structure. Please correct me if I am wrong.
>This could be a solution, though it will be another cache line access. It might be ok given that it is a single cache line for entire hash
>table.
[Wang, Yipeng] Yeah that is what I meant. It is an additional memory access but probably it will be in local cache.
Since time is tight, it could be a simple workaround for this version and in future you can extend this pointed counter to a counter array as Ola suggested and the
Cuckooo switch paper did for scaling issue.
>
>> IMO, DPDK should have guidelines on how to handle the API compatibility
>> breaks. I will send an email to tech board on this.
>> We can also solve this by having counters on the bucket. I was planning to do
>> this little bit later. I will look at the effort involved and may be do it now.
next prev parent reply other threads:[~2018-10-04 19:16 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-06 17:12 [dpdk-dev] [PATCH 0/4] Address reader-writer concurrency in rte_hash Honnappa Nagarahalli
2018-09-06 17:12 ` [dpdk-dev] [PATCH 1/4] hash: correct key store element alignment Honnappa Nagarahalli
2018-09-27 23:58 ` Wang, Yipeng1
2018-09-06 17:12 ` [dpdk-dev] [PATCH 2/4] hash: add memory ordering to avoid race conditions Honnappa Nagarahalli
2018-09-28 0:43 ` Wang, Yipeng1
2018-09-30 22:20 ` Honnappa Nagarahalli
2018-10-01 22:41 ` Wang, Yipeng1
2018-10-01 10:42 ` Ola Liljedahl
2018-10-02 1:52 ` Wang, Yipeng1
2018-09-06 17:12 ` [dpdk-dev] [PATCH 3/4] hash: fix rw concurrency while moving keys Honnappa Nagarahalli
2018-09-28 1:00 ` Wang, Yipeng1
2018-09-28 8:26 ` Bruce Richardson
2018-09-28 8:55 ` Van Haaren, Harry
2018-09-30 22:33 ` Honnappa Nagarahalli
2018-10-02 13:17 ` Van Haaren, Harry
2018-10-02 23:58 ` Wang, Yipeng1
2018-10-03 17:32 ` Honnappa Nagarahalli
2018-10-03 17:56 ` Wang, Yipeng1
2018-10-03 23:05 ` Ola Liljedahl
2018-10-04 3:32 ` Honnappa Nagarahalli
2018-10-04 3:54 ` Honnappa Nagarahalli
2018-10-04 19:16 ` Wang, Yipeng1 [this message]
2018-09-30 23:05 ` Honnappa Nagarahalli
2018-10-01 22:56 ` Wang, Yipeng1
2018-10-03 0:16 ` Wang, Yipeng1
2018-10-03 17:39 ` Honnappa Nagarahalli
2018-09-06 17:12 ` [dpdk-dev] [PATCH 4/4] hash: enable lock-free reader-writer concurrency Honnappa Nagarahalli
2018-09-28 1:33 ` Wang, Yipeng1
2018-10-01 4:11 ` Honnappa Nagarahalli
2018-10-01 23:54 ` Wang, Yipeng1
2018-10-11 5:24 ` Honnappa Nagarahalli
2018-09-14 21:18 ` [dpdk-dev] [PATCH 0/4] Address reader-writer concurrency in rte_hash Honnappa Nagarahalli
2018-09-26 14:36 ` Honnappa Nagarahalli
2018-09-27 23:45 ` Wang, Yipeng1
2018-09-28 21:11 ` Honnappa Nagarahalli
2018-10-02 0:30 ` Wang, Yipeng1
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