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From: Neil Horman <nhorman@tuxdriver.com>
To: "Richardson, Bruce" <bruce.richardson@intel.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH 3/5] testpmd: Change rxfreet default to 32
Date: Fri, 19 Sep 2014 11:18:50 -0400
Message-ID: <20140919151850.GD12897@hmsreliant.think-freely.org> (raw)
In-Reply-To: <59AF69C657FD0841A61C55336867B5B0343F395C@IRSMSX103.ger.corp.intel.com>

On Fri, Sep 19, 2014 at 10:28:31AM +0000, Richardson, Bruce wrote:
> 
> 
> > -----Original Message-----
> > From: Neil Horman [mailto:nhorman@tuxdriver.com]
> > Sent: Friday, September 19, 2014 11:25 AM
> > To: Richardson, Bruce
> > Cc: Thomas Monjalon; dev@dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH 3/5] testpmd: Change rxfreet default to 32
> > 
> > On Fri, Sep 19, 2014 at 09:18:26AM +0000, Richardson, Bruce wrote:
> > > > -----Original Message-----
> > > > From: Neil Horman [mailto:nhorman@tuxdriver.com]
> > > > Sent: Thursday, September 18, 2014 7:09 PM
> > > > To: Thomas Monjalon
> > > > Cc: Richardson, Bruce; dev@dpdk.org
> > > > Subject: Re: [dpdk-dev] [PATCH 3/5] testpmd: Change rxfreet default to 32
> > > >
> > > > On Thu, Sep 18, 2014 at 07:13:52PM +0200, Thomas Monjalon wrote:
> > > > > 2014-09-18 15:53, Richardson, Bruce:
> > > > > > > > --- a/app/test-pmd/testpmd.c
> > > > > > > > +++ b/app/test-pmd/testpmd.c
> > > > > > > > @@ -225,7 +225,7 @@ struct rte_eth_thresh tx_thresh = {
> > > > > > > >  /*
> > > > > > > >   * Configurable value of RX free threshold.
> > > > > > > >   */
> > > > > > > > -uint16_t rx_free_thresh = 0; /* Immediately free RX descriptors by
> > > > default. */
> > > > > > > > +uint16_t rx_free_thresh = 32; /* Refill RX descriptors once every 32
> > > > packets
> > > > > > > */
> > > > > > > >
> > > > > > >
> > > > > > > Why 32?  Was that an experimentally determined value?
> > > > > > > Does it hold true for all PMD's?
> > > > > >
> > > > > > This is primarily for the ixgbe PMD, which is right now the most
> > > > > > highly tuned driver, but it works fine for all other ones too,
> > > > > > as far as I'm aware.
> > > > >
> > > > > Yes, you are changing this value for all PMDs but you're targetting
> > > > > only one.
> > > > > These thresholds are dependent of the PMD implementation. There's
> > > > > something wrong here.
> > > > >
> > > > I agree. Its fine to do this, but it does seem like the sample application
> > > > should document why it does this and make note of the fact that other PMDs
> > > > may
> > > > have a separate optimal value.
> > > >
> > > > > > Basically, this is the minimum setting needed to enable either the
> > > > > > bulk alloc or vector RX routines inside the ixgbe driver, so it's
> > > > > > best made the default for that reason. Please see
> > > > > > "check_rx_burst_bulk_alloc_preconditions()" in ixgbe_rxtx.c, and
> > > > > > RX function assignment logic in "ixgbe_dev_rx_queue_setup()" in
> > > > > > the same file.
> > > > >
> > > > > Since this parameter is so important, it could be a default value
> > somewhere.
> > > > >
> > > > > I think we should split generic tuning parameters and tuning parameters
> > > > > related to driver implementation or specific hardware.
> > > > > Then we should provide some good default values for each of them.
> > > > > At last, if needed, applications should be able to easily tune the
> > > > > pmd-specific parameters.
> > > > >
> > > > I like this idea.  I've not got an idea of how much work it is to do so, but in
> > > > principle it makes sense.
> > > >
> > > > Perhaps for the immediate need, since rte_eth_rx_queue_setup allows the
> > > > config
> > > > struct to get passed directly to PMDs, we can create a reserved value
> > > > RTE_ETH_RX_FREE_THRESH_OPTIMAL, that instructs the pmd to select
> > > > whatever
> > > > threshold is optimal for its own hardware?
> > > >
> > > > Neil
> > > >
> > > Actually, looking at the code, I would suggest a couple of options, some of
> > which may be used together.
> > > 	1) we make NULL a valid value for the rxconf structure parameter to
> > rte_eth_rx_queue_setup. There is little information in it that should really need
> > to be passed in by applications to the drivers, and that would allow the drivers to
> > be completely free to select the best options for their own operation.
> > > 	2) As a companion to that (or as an alternative), we could also allow
> > each driver to provide its own functions for rte_eth_get_rxconf_default, and
> > rte_eth_get_txconf_default, to be used by applications that want to use known-
> > good values for thresholds but also want to tweak one of the other values e.g.
> > for rx, set the drop_en bit, and for tx set the txqflags to disable offloads.
> > > 	3) Lastly, we could also consider removing the threshold and other not-
> > generally-used values from the rxconf and txconf structures and make those
> > removed fields completely driver-set values. Optionally, we could provide an
> > alternate API to tune them, but I don't really see this being useful in most cases,
> > and I'd probably omit it unless someone can prove a need for such APIs.
> > >
> > These all sound fairly reasonable to me.
> > Neil
> 
> Further thinking seems to me like 1 doesn't really go very far, so it falls between 2 and 3. Any preference between them?
> 
Not to answer a question with a question, but, because I'm not really sure, how
much does an application really need to know or set in regards to hardware queue
parameters.  I ask because I'm inclined to just go with option 3 (since it
prevents expansion of the application visible API), but I'm not sure if theres
important functionality you loose in doing so.

Neil

> /Bruce
> 

  reply	other threads:[~2014-09-19 15:13 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-09-17 10:01 [dpdk-dev] [PATCH 0/5] Mbuf Structure Rework, part 3 Bruce Richardson
2014-09-17 10:01 ` [dpdk-dev] [PATCH 1/5] mbuf: ensure next pointer is set to null on free Bruce Richardson
2014-09-17 10:01 ` [dpdk-dev] [PATCH 2/5] ixgbe: add prefetch to improve slow-path tx perf Bruce Richardson
2014-09-17 15:21   ` Neil Horman
2014-09-17 15:35     ` Richardson, Bruce
2014-09-17 17:59       ` Neil Horman
2014-09-18 13:36         ` Bruce Richardson
2014-09-18 15:29           ` Neil Horman
2014-09-18 15:42             ` Bruce Richardson
2014-09-18 17:56               ` Neil Horman
2014-09-17 10:01 ` [dpdk-dev] [PATCH 3/5] testpmd: Change rxfreet default to 32 Bruce Richardson
2014-09-17 15:29   ` Neil Horman
2014-09-18 15:53     ` Richardson, Bruce
2014-09-18 17:13       ` Thomas Monjalon
2014-09-18 18:08         ` Neil Horman
2014-09-19  9:18           ` Richardson, Bruce
2014-09-19 10:24             ` Neil Horman
2014-09-19 10:28               ` Richardson, Bruce
2014-09-19 15:18                 ` Neil Horman [this message]
2014-09-18 18:03       ` Neil Horman
2014-09-17 10:01 ` [dpdk-dev] [PATCH 4/5] mbuf: add userdata pointer field Bruce Richardson
2014-09-17 15:35   ` Neil Horman
2014-09-17 16:02     ` Richardson, Bruce
2014-09-17 18:29       ` Neil Horman
2014-09-17 10:01 ` [dpdk-dev] [PATCH 5/5] mbuf: Add in second vlan tag field to mbuf Bruce Richardson
2014-09-17 20:46   ` Stephen Hemminger
2014-09-23 11:08 ` [dpdk-dev] [PATCH v2 0/5] Mbuf Structure Rework, part 3 Bruce Richardson
2014-09-23 11:08   ` [dpdk-dev] [PATCH v2 1/5] mbuf: ensure next pointer is set to null on free Bruce Richardson
2014-09-23 11:08   ` [dpdk-dev] [PATCH v2 2/5] ixgbe: add prefetch to improve slow-path tx perf Bruce Richardson
2014-09-23 11:08   ` [dpdk-dev] [PATCH v2 3/5] testpmd: Change rxfreet default to 32 Bruce Richardson
2014-09-23 17:02     ` Neil Horman
2014-09-24  9:03       ` Richardson, Bruce
2014-09-24 10:05         ` Neil Horman
2014-11-07 12:30         ` Thomas Monjalon
2014-11-07 13:49           ` Bruce Richardson
2014-09-23 11:08   ` [dpdk-dev] [PATCH v2 4/5] mbuf: add userdata pointer field Bruce Richardson
2014-09-23 11:08   ` [dpdk-dev] [PATCH v2 5/5] mbuf: switch vlan_tci and reserved2 fields Bruce Richardson
2014-09-29 15:58   ` [dpdk-dev] [PATCH v2 0/5] Mbuf Structure Rework, part 3 De Lara Guarch, Pablo
2014-10-08 12:31     ` Thomas Monjalon

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