From: Bruce Richardson <bruce.richardson@intel.com>
To: dev@dpdk.org
Cc: Helin Zhang <helin.zhang@intel.com>, Jingjing Wu <jingjing.wu@intel.com>
Subject: Re: [dpdk-dev] [PATCH] i40e: improve performance of vector PMD
Date: Thu, 14 Apr 2016 14:50:24 +0100 [thread overview]
Message-ID: <20160414135024.GA25840@bricha3-MOBL3> (raw)
In-Reply-To: <1460628921-25635-1-git-send-email-bruce.richardson@intel.com>
On Thu, Apr 14, 2016 at 11:15:21AM +0100, Bruce Richardson wrote:
> An analysis of the i40e code using Intel® VTune™ Amplifier 2016 showed
> that the code was unexpectedly causing stalls due to "Loads blocked by
> Store Forwards". This can occur when a load from memory has to wait
> due to the prior store being to the same address, but being of a smaller
> size i.e. the stored value cannot be directly returned to the loader.
> [See ref: https://software.intel.com/en-us/node/544454]
>
> These stalls are due to the way in which the data_len values are handled
> in the driver. The lengths are extracted using vector operations, but those
> 16-bit lengths are then assigned using scalar operations i.e. 16-bit
> stores.
>
> These regular 16-bit stores actually have two effects in the code:
> * they cause the "Loads blocked by Store Forwards" issues reported
> * they also cause the previous loads in the RX function to actually be a
> load followed by a store to an address on the stack, because the 16-bit
> assignment can't be done to an xmm register.
>
> By converting the 16-bit stores operations into a sequence of SSE blend
> operations, we can ensure that the descriptor loads only occur once, and
> avoid both the additional store and loads from the stack, as well as the
> stalls due to the second loads being blocked.
>
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
>
Self-NAK on this version. The blend instruction used is SSE4.1 so breaks the
"default" build.
Two obvious options to fix this:
1. Keep the old code with SSE4.1 #ifdefs separating old and new
2. Update the vpmd requirement to SSE4.1, and factor that in during runtime
select of the RX code path.
Personally, I prefer the second option. Any objections?
/Bruce
next prev parent reply other threads:[~2016-04-14 13:50 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-14 10:15 Bruce Richardson
2016-04-14 13:50 ` Bruce Richardson [this message]
2016-04-14 14:00 ` Ananyev, Konstantin
2016-04-14 15:33 ` Iremonger, Bernard
2016-04-14 16:02 ` [dpdk-dev] [PATCH v2 0/3] improve i40e vpmd Bruce Richardson
2016-04-14 16:02 ` [dpdk-dev] [PATCH v2 1/3] i40e: require SSE4.1 support for vector driver Bruce Richardson
2016-04-14 16:02 ` [dpdk-dev] [PATCH v2 2/3] i40e: improve performance of vector PMD Bruce Richardson
2016-04-14 16:02 ` [dpdk-dev] [PATCH v2 3/3] i40e: simplify SSE packet length extraction code Bruce Richardson
2016-04-17 8:32 ` [dpdk-dev] [PATCH v2 0/3] improve i40e vpmd Zhe Tao
2016-04-27 16:30 ` Bruce Richardson
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=20160414135024.GA25840@bricha3-MOBL3 \
--to=bruce.richardson@intel.com \
--cc=dev@dpdk.org \
--cc=helin.zhang@intel.com \
--cc=jingjing.wu@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
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).