From: "Van Haaren, Harry" <harry.van.haaren@intel.com>
To: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
Phil Yang <Phil.Yang@arm.com>, "dev@dpdk.org" <dev@dpdk.org>
Cc: "thomas@monjalon.net" <thomas@monjalon.net>,
"david.marchand@redhat.com" <david.marchand@redhat.com>,
"Ananyev, Konstantin" <konstantin.ananyev@intel.com>,
"jerinj@marvell.com" <jerinj@marvell.com>,
"hemant.agrawal@nxp.com" <hemant.agrawal@nxp.com>,
Gavin Hu <Gavin.Hu@arm.com>, nd <nd@arm.com>,
"stable@dpdk.org" <stable@dpdk.org>,
"Eads, Gage" <gage.eads@intel.com>,
"Richardson, Bruce" <bruce.richardson@intel.com>, nd <nd@arm.com>
Subject: Re: [dpdk-stable] [PATCH v2 1/6] service: fix race condition for MT unsafe service
Date: Fri, 1 May 2020 14:21:53 +0000 [thread overview]
Message-ID: <BYAPR11MB3143A5D709436F9D55B64EDCD7AB0@BYAPR11MB3143.namprd11.prod.outlook.com> (raw)
In-Reply-To: <DBBPR08MB4646F542ABAC37DB1FE8166598AD0@DBBPR08MB4646.eurprd08.prod.outlook.com>
> -----Original Message-----
> From: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
> Sent: Wednesday, April 29, 2020 11:49 PM
> To: Van Haaren, Harry <harry.van.haaren@intel.com>; Phil Yang
> <Phil.Yang@arm.com>; dev@dpdk.org
> Cc: thomas@monjalon.net; david.marchand@redhat.com; Ananyev, Konstantin
> <konstantin.ananyev@intel.com>; jerinj@marvell.com;
> hemant.agrawal@nxp.com; Gavin Hu <Gavin.Hu@arm.com>; nd
> <nd@arm.com>; stable@dpdk.org; Eads, Gage <gage.eads@intel.com>;
> Richardson, Bruce <bruce.richardson@intel.com>; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>; nd <nd@arm.com>
> Subject: RE: [PATCH v2 1/6] service: fix race condition for MT unsafe service
>
> Hi Harry,
> Thanks for getting back on this.
>
> <snip>
>
> > > Subject: [PATCH v2 1/6] service: fix race condition for MT unsafe
> > > service
> > >
> > > From: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> > >
> > > The MT unsafe service might get configured to run on another core
> > > while the service is running currently. This might result in the MT
> > > unsafe service running on multiple cores simultaneously. Use
> > > 'execute_lock' always when the service is MT unsafe.
> > >
> > > Fixes: e9139a32f6e8 ("service: add function to run on app lcore")
> > > Cc: stable@dpdk.org
> > >
> > > Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> > > Reviewed-by: Phil Yang <phil.yang@arm.com>
> > > ---
> >
> > Thanks for spinning a new revision - based on ML discussion previously, it
> > seems like the "use service-run-count" to avoid this race would be a complex
> > solution.
> >
> > Suggesting the following;
> > 1) Take the approach as per this patch, to always take the atomic, fixing the
> > race condition.
> Ok
I've micro-benchmarked this code change inside the service cores autotest, and it
introduces around 35 cycles of overhead per service call. This is not ideal, but given
it's a bugfix, and by far the simplest method to fix this race-condition. Having
discussed and investigated multiple other solutions, I believe this is the right solution.
Thanks Honnappa and Phil for identifying and driving a solution.
I suggest to post the benchmarking unit-test addition patch, and integrate that
*before* the series under review here gets merged? This makes benchmarking
of the "before bugfix" performance in future easier should it be required.
> > 2) Add an API to service-cores, which allows "committing" of mappings.
> > Committing the mapping would imply that the mappings will not be changed
> > in future. With runtime-remapping being removed from the equation, the
> > existing branch-over-atomic optimization is valid again.
> Ok. Just to make sure I understand this:
> a) on the data plane, if commit API is called (probably a new state variable) and
> num_mapped_cores is set to 1, there is no need to take the lock.
> b) possible implementation of the commit API would check if
> num_mapped_cores for the service is set to 1 and set a variable to indicate that
> the lock is not required.
>
> What do you think about asking the application to set the service capability to
> MT_SAFE if it knows that the service will run on a single core? This would
> require us to change the documentation and does not require additional code.
That's a nice idea - I like that if applications want to micro-optimize around
the atomic, that they have a workaround/solution to do so, particularly that it
doesn't require code-changes and backporting.
Will send review and send feedback on the patches themselves.
Regards, -Harry
> > So this would offer applications two situations
> > A) No application change: possible performance regression due to atomic
> > always taken.
> > B) Call "commit" API, and regain the performance as per previous DPDK
> > versions.
> >
> > Thoughts/opinions on the above? I've flagged the rest of the patchset for
> > review ASAP. Regards, -Harry
> >
> > > lib/librte_eal/common/rte_service.c | 11 +++++------
> > > 1 file changed, 5 insertions(+), 6 deletions(-)
<snip patch changes>
next prev parent reply other threads:[~2020-05-01 14:22 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1583862551-2049-1-git-send-email-phil.yang@arm.com>
2020-03-10 17:49 ` [dpdk-stable] [PATCH 05/10] service: remove rte prefix from static functions Phil Yang
2020-03-10 17:49 ` [dpdk-stable] [PATCH 06/10] service: remove redundant code Phil Yang
2020-03-10 17:49 ` [dpdk-stable] [PATCH 07/10] service: avoid race condition for MT unsafe service Phil Yang
2020-03-10 17:49 ` [dpdk-stable] [PATCH 08/10] service: identify service running on another core correctly Phil Yang
[not found] ` <1583993624-20446-1-git-send-email-phil.yang@arm.com>
2020-03-12 6:13 ` [dpdk-stable] [PATCH v2 05/10] service: remove rte prefix from static functions Phil Yang
2020-03-12 6:13 ` [dpdk-stable] [PATCH v2 06/10] service: remove redundant code Phil Yang
2020-03-12 6:13 ` [dpdk-stable] [PATCH v2 07/10] service: avoid race condition for MT unsafe service Phil Yang
2020-03-12 6:13 ` [dpdk-stable] [PATCH v2 08/10] service: identify service running on another core correctly Phil Yang
[not found] ` <1583999071-22872-1-git-send-email-phil.yang@arm.com>
2020-03-12 7:44 ` [dpdk-stable] [PATCH v2 05/10] service: remove rte prefix from static functions Phil Yang
2020-03-12 7:44 ` [dpdk-stable] [PATCH v2 06/10] service: remove redundant code Phil Yang
2020-03-12 7:44 ` [dpdk-stable] [PATCH v2 07/10] service: avoid race condition for MT unsafe service Phil Yang
2020-03-12 7:44 ` [dpdk-stable] [PATCH v2 08/10] service: identify service running on another core correctly Phil Yang
[not found] ` <1584407863-774-1-git-send-email-phil.yang@arm.com>
2020-03-17 1:17 ` [dpdk-stable] [PATCH v3 07/12] service: remove rte prefix from static functions Phil Yang
2020-04-03 11:57 ` Van Haaren, Harry
2020-04-08 10:14 ` Phil Yang
2020-04-08 10:36 ` Van Haaren, Harry
2020-04-08 10:49 ` Phil Yang
2020-04-05 21:35 ` Honnappa Nagarahalli
2020-04-08 10:14 ` Phil Yang
[not found] ` <1587659482-27133-1-git-send-email-phil.yang@arm.com>
2020-04-23 16:31 ` [dpdk-stable] [PATCH v2 1/6] service: fix race condition for MT unsafe service Phil Yang
2020-04-29 16:51 ` Van Haaren, Harry
2020-04-29 22:48 ` Honnappa Nagarahalli
2020-05-01 14:21 ` Van Haaren, Harry [this message]
2020-05-01 14:56 ` Honnappa Nagarahalli
2020-05-01 17:51 ` Van Haaren, Harry
2020-04-23 16:31 ` [dpdk-stable] [PATCH v2 2/6] service: identify service running on another core correctly Phil Yang
[not found] ` <20200502000245.11071-1-honnappa.nagarahalli@arm.com>
2020-05-02 0:02 ` [dpdk-stable] [PATCH v3 1/6] service: fix race condition for MT unsafe service Honnappa Nagarahalli
2020-05-05 14:48 ` Van Haaren, Harry
2020-05-02 0:02 ` [dpdk-stable] [PATCH v3 2/6] service: identify service running on another core correctly Honnappa Nagarahalli
2020-05-05 14:48 ` Van Haaren, Harry
[not found] ` <20200505211732.25291-1-honnappa.nagarahalli@arm.com>
2020-05-05 21:17 ` [dpdk-stable] [PATCH v4 1/6] service: fix race condition for MT unsafe service Honnappa Nagarahalli
2020-05-05 21:17 ` [dpdk-stable] [PATCH v4 2/6] service: fix identification of service running on other lcore Honnappa Nagarahalli
[not found] ` <1588760683-11027-1-git-send-email-phil.yang@arm.com>
2020-05-06 10:24 ` [dpdk-stable] [PATCH v5 1/6] service: fix race condition for MT unsafe service Phil Yang
2020-05-06 10:24 ` [dpdk-stable] [PATCH v5 2/6] service: fix identification of service running on other lcore Phil Yang
[not found] ` <1588778884-13047-1-git-send-email-phil.yang@arm.com>
2020-05-06 15:27 ` [dpdk-stable] [PATCH v6 1/6] service: fix race condition for MT unsafe service Phil Yang
2020-05-06 15:28 ` [dpdk-stable] [PATCH v6 2/6] service: fix identification of service running on other lcore Phil Yang
2020-03-17 1:17 ` [dpdk-stable] [PATCH v3 08/12] service: remove redundant code Phil Yang
2020-04-03 11:58 ` Van Haaren, Harry
2020-04-05 18:35 ` Honnappa Nagarahalli
2020-04-08 10:15 ` Phil Yang
2020-03-17 1:17 ` [dpdk-stable] [PATCH v3 09/12] service: avoid race condition for MT unsafe service Phil Yang
2020-04-03 11:58 ` Van Haaren, Harry
2020-04-04 18:03 ` Honnappa Nagarahalli
2020-04-08 18:05 ` Van Haaren, Harry
2020-04-09 1:31 ` Honnappa Nagarahalli
2020-04-09 16:46 ` Van Haaren, Harry
2020-04-18 6:21 ` Honnappa Nagarahalli
2020-04-21 17:43 ` Van Haaren, Harry
2020-03-17 1:17 ` [dpdk-stable] [PATCH v3 10/12] service: identify service running on another core correctly Phil Yang
2020-04-03 11:58 ` Van Haaren, Harry
2020-04-05 2:43 ` Honnappa Nagarahalli
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=BYAPR11MB3143A5D709436F9D55B64EDCD7AB0@BYAPR11MB3143.namprd11.prod.outlook.com \
--to=harry.van.haaren@intel.com \
--cc=Gavin.Hu@arm.com \
--cc=Honnappa.Nagarahalli@arm.com \
--cc=Phil.Yang@arm.com \
--cc=bruce.richardson@intel.com \
--cc=david.marchand@redhat.com \
--cc=dev@dpdk.org \
--cc=gage.eads@intel.com \
--cc=hemant.agrawal@nxp.com \
--cc=jerinj@marvell.com \
--cc=konstantin.ananyev@intel.com \
--cc=nd@arm.com \
--cc=stable@dpdk.org \
--cc=thomas@monjalon.net \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).