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From: Neil Horman <nhorman@tuxdriver.com>
To: Thomas Monjalon <thomas.monjalon@6wind.com>
Cc: dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH 3/5] testpmd: Change rxfreet default to 32
Date: Thu, 18 Sep 2014 14:08:41 -0400
Message-ID: <20140918180841.GN20389@hmsreliant.think-freely.org> (raw)
In-Reply-To: <3289751.t83Qqk3rkH@xps13>

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

> Thoughts?
> 
> -- 
> Thomas
> 

  reply	other threads:[~2014-09-18 18:03 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 [this message]
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
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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