From: Jerin Jacob <jerin.jacob@caviumnetworks.com>
To: Bruce Richardson <bruce.richardson@intel.com>
Cc: <dev@dpdk.org>, <thomas.monjalon@6wind.com>,
<konstantin.ananyev@intel.com>, <viktorin@rehivetech.com>,
<jianbo.liu@linaro.org>
Subject: Re: [dpdk-dev] [PATCH] mbuf: make rearm_data address naturally aligned
Date: Thu, 19 May 2016 00:20:16 +0530 [thread overview]
Message-ID: <20160518185011.GA4432@localhost.localdomain> (raw)
In-Reply-To: <20160518164300.GA12324@bricha3-MOBL3>
On Wed, May 18, 2016 at 05:43:00PM +0100, Bruce Richardson wrote:
> On Wed, May 18, 2016 at 07:27:43PM +0530, Jerin Jacob wrote:
> > To avoid multiple stores on fast path, Ethernet drivers
> > aggregate the writes to data_off, refcnt, nb_segs and port
> > to an uint64_t data and write the data in one shot
> > with uint64_t* at &mbuf->rearm_data address.
> >
> > Some of the non-IA platforms have store operation overhead
> > if the store address is not naturally aligned.This patch
> > fixes the performance issue on those targets.
> >
> > Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> > ---
> >
> > Tested this patch on IA and non-IA(ThunderX) platforms.
> > This patch shows 400Kpps/core improvement on ThunderX + ixgbe + vector environment.
> > and this patch does not have any overhead on IA platform.
> >
> > Have tried an another similar approach by replacing "buf_len" with "pad"
> > (in this patch context),
> > Since it has additional overhead on read and then mask to keep "buf_len" intact,
> > not much improvement is not shown.
> > ref: http://dpdk.org/ml/archives/dev/2016-May/038914.html
> >
> > ---
> While this will work and from your tests doesn't seem to have a performance
> impact, I'm not sure I particularly like it. It's extending out the end of
> cacheline0 of the mbuf by 16 bytes, though I suppose it's not technically using
> up any more space of it.
Extending by 2 bytes. Right ?. Yes, I guess, Now we using only 56 out of 64 bytes
in the first 64-byte cache line.
>
> What I'm wondering about though, is do we have any usecases where we need a
> variable buf_len for packets for RX. These mbufs come directly from a mempool,
> which is generally understood to be a set of fixed-sized buffers. I realise that
> this change was made in the past after some discussion, but one of the key points
> there [at least to my reading] was that - even though nobody actually made a
> concrete case where they had variable-sized buffers - having support for them
> made no performance difference.
>
> The latter part of that has now changed, and supporting variable-sized mbufs
> from an mbuf pool has a perf impact. Do we definitely need that functionality,
> because the easiest fix here is just to move the rxrearm marker back above
> mbuf_len as it was originally in releases like 1.8?
And initialize the buf_len with mp->elt_size - sizeof(struct rte_mbuf).
Right?
I don't have a strong opinion on this, I can do this if there is no
objection on this. Let me know.
However, I do see in future, "buf_len" may belong at the end of the first 64 byte
cache line as currently "port" is defined as uint8_t, IMO, that is less.
We may need to increase that uint16_t. The reason why I think that
because, Currently in ThunderX HW, we do have 128VFs per socket for
built-in NIC, So, the two node configuration and one external PCIe NW card
configuration can easily go beyond 256 ports.
>
> Regards,
> /Bruce
>
> Ref: http://dpdk.org/ml/archives/dev/2014-December/009432.html
>
next prev parent reply other threads:[~2016-05-18 18:50 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-18 13:57 Jerin Jacob
2016-05-18 16:43 ` Bruce Richardson
2016-05-18 18:50 ` Jerin Jacob [this message]
2016-05-19 8:50 ` Bruce Richardson
2016-05-19 11:54 ` Jan Viktorin
2016-05-19 12:18 ` Ananyev, Konstantin
2016-05-19 13:35 ` Jerin Jacob
2016-05-19 15:50 ` Thomas Monjalon
2016-05-23 11:19 ` Olivier Matz
2016-07-04 12:45 ` Jerin Jacob
2016-07-04 12:58 ` Olivier MATZ
2016-05-20 15:30 ` Zoltan Kiss
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=20160518185011.GA4432@localhost.localdomain \
--to=jerin.jacob@caviumnetworks.com \
--cc=bruce.richardson@intel.com \
--cc=dev@dpdk.org \
--cc=jianbo.liu@linaro.org \
--cc=konstantin.ananyev@intel.com \
--cc=thomas.monjalon@6wind.com \
--cc=viktorin@rehivetech.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).