From: Stephen Hemminger <stephen@networkplumber.org>
To: "Mattias Rönnblom" <hofors@lysator.liu.se>
Cc: Bruce Richardson <bruce.richardson@intel.com>,
dev@dpdk.org, Jerin Jacob <jerinj@marvell.com>
Subject: Re: [RFC PATCH] eventdev: ensure 16-byte alignment for events
Date: Fri, 19 Jan 2024 14:30:41 -0800 [thread overview]
Message-ID: <20240119143041.59802717@hermes.local> (raw)
In-Reply-To: <fcd11d73-d098-4734-9540-944aff73ed71@lysator.liu.se>
On Fri, 6 Oct 2023 14:15:00 +0200
Mattias Rönnblom <hofors@lysator.liu.se> wrote:
> On 2023-10-05 13:51, Bruce Richardson wrote:
> > The event structure in DPDK is 16-bytes in size, and events are
> > regularly passed as parameters directly rather than being passed as
> > pointers.
>
> When are events passed by-value, rather than by-reference? There are no
> such examples in the public eventdev API.
>
> To help compiler optimize correctly, we can explicitly request
> > 16-byte alignment for events, which means that we should be able
> > to do aligned vector loads/stores (e.g. with SSE or Neon) when working
> > with those events.
> >
>
> That change is both helping and sabotaging the optimizer's work. Now
> every stack allocation needs to be 2-byte aligned - in DPDK code, and in
> the application.
>
> The effect this change has on an eventdev app using DSW is a ~3
> cycle/event performance degradation on an AMD Zen 3 system, and a ~4
> cycle/event performance degradation on a Skylake-generation Intel CPU.
>
> What scenarios do you have in mind, where this change would improve the
> generated code? Something where there are no unaligned loads available
> in the ISA, or they are much slower than their aligned counterparts?
>
> When I looked into the same issue for the DPDK IP checksumming routines,
> there basically were no such. Not that I could find.
>
> > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Don't understand what the issue is. Isn't the event structure typically
on stack. Adding padding there would not help.
prev parent reply other threads:[~2024-01-19 22:30 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-05 11:51 Bruce Richardson
2023-10-05 12:06 ` Bruce Richardson
2023-10-05 13:11 ` Jerin Jacob
2023-10-05 13:15 ` Bruce Richardson
2023-10-06 7:19 ` Jerin Jacob
2023-10-05 12:12 ` Morten Brørup
2023-10-05 13:02 ` Bruce Richardson
2023-10-06 9:37 ` [PATCH v2] " Bruce Richardson
2023-10-06 9:45 ` [PATCH v3] " Bruce Richardson
2023-10-06 10:13 ` Morten Brørup
2023-10-06 10:16 ` Jerin Jacob
2023-10-06 10:19 ` Bruce Richardson
2023-10-06 10:24 ` Jerin Jacob
2023-10-06 10:27 ` Bruce Richardson
2023-10-06 10:16 ` Bruce Richardson
2023-10-06 10:35 ` Morten Brørup
2023-10-06 10:44 ` Bruce Richardson
2023-10-06 10:29 ` [PATCH v4] " Bruce Richardson
2023-11-12 0:01 ` Stephen Hemminger
2023-11-12 8:30 ` Morten Brørup
2023-11-12 23:31 ` Stephen Hemminger
2023-11-13 7:58 ` Morten Brørup
2024-01-19 21:05 ` Tyler Retzlaff
2023-10-06 12:15 ` [RFC PATCH] " Mattias Rönnblom
2023-10-06 12:19 ` Bruce Richardson
2023-10-06 12:29 ` Mattias Rönnblom
2024-01-19 22:30 ` Stephen Hemminger [this message]
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