DPDK patches and discussions
 help / color / mirror / Atom feed
From: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: Yipeng Wang <yipeng1.wang@intel.com>,
	Sameh Gobriel <sameh.gobriel@intel.com>,
	Bruce Richardson <bruce.richardson@intel.com>,
	"dev@dpdk.org" <dev@dpdk.org>,
	"pablo.de.lara.guarch@intel.com" <pablo.de.lara.guarch@intel.com>,
	nd <nd@arm.com>,
	Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
	nd <nd@arm.com>
Subject: Re: [dpdk-dev] [PATCH] hash: document breakage with multi-writer thread
Date: Thu, 4 Jun 2020 18:43:36 +0000
Message-ID: <AM4PR0802MB22129FFB7504E7161E68B6B998890@AM4PR0802MB2212.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <20200604105817.1a3a2749@hermes.lan>

> > <snip>
> >
> > > Subject: [PATCH] hash: document breakage with multi-writer thread
> > >
> > > The code in rte_cuckoo_hash multi-writer support is broken if write
> > > operations are called from a non-EAL thread.
> > >
> > > rte_lcore_id() wil return LCORE_ID_ANY (UINT32_MAX) for non EAL
> > > thread and that leads to using wrong local cache.
> > >
> > > Add error checks and document the restriction.
> > Having multiple non-EAL writer threads is a valid use case. Should we fix the
> issue instead?
> 
> Discovered this the hard way...
> 
> Fixing is non-trivial. Basically, the local cache has to be take out and that
> leads to having to do real locking or atomic operations.
Looking at rte_hash_create function:

        if (params->extra_flag & RTE_HASH_EXTRA_FLAGS_MULTI_WRITER_ADD) {
                use_local_cache = 1;
                writer_takes_lock = 1;
        }

The writer locks are in place already. The code to handle the case when local cache is taken out is also there.
What we need is another input flag that says 'multi writer + non-eal threads' which would set 'use_local_cache = 0' and 'writer_takes_lock = 1'.
Not sure, it would be valuable addition. But looks like this is what you were expecting when you had enabled 'RTE_HASH_EXTRA_FLAGS_MULTI_WRITER_ADD'. Many other APIs in DPDK do not provide this kind of MT safety.

  reply	other threads:[~2020-06-04 18:43 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-04 17:17 Stephen Hemminger
2020-06-04 17:51 ` Honnappa Nagarahalli
2020-06-04 17:58   ` Stephen Hemminger
2020-06-04 18:43     ` Honnappa Nagarahalli [this message]
2020-06-04 19:10       ` Wang, Yipeng1
2020-06-04 19:34         ` Honnappa Nagarahalli
2020-06-04 20:22           ` Wang, Yipeng1
2020-06-04 21:06             ` Stephen Hemminger
2020-06-04 21:32 ` Wang, Yipeng1
2020-06-05 18:35 ` Stephen Hemminger
2020-06-16 16:12   ` Thomas Monjalon
2020-11-26 17:56     ` Thomas Monjalon

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=AM4PR0802MB22129FFB7504E7161E68B6B998890@AM4PR0802MB2212.eurprd08.prod.outlook.com \
    --to=honnappa.nagarahalli@arm.com \
    --cc=bruce.richardson@intel.com \
    --cc=dev@dpdk.org \
    --cc=nd@arm.com \
    --cc=pablo.de.lara.guarch@intel.com \
    --cc=sameh.gobriel@intel.com \
    --cc=stephen@networkplumber.org \
    --cc=yipeng1.wang@intel.com \
    /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

DPDK patches and discussions

This inbox may be cloned and mirrored by anyone:

	git clone --mirror https://inbox.dpdk.org/dev/0 dev/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 dev dev/ https://inbox.dpdk.org/dev \
		dev@dpdk.org
	public-inbox-index dev

Example config snippet for mirrors.
Newsgroup available over NNTP:
	nntp://inbox.dpdk.org/inbox.dpdk.dev


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git