From: "Mattias Rönnblom" <hofors@lysator.liu.se>
To: Bruce Richardson <bruce.richardson@intel.com>, dev@dpdk.org
Cc: Jerin Jacob <jerinj@marvell.com>
Subject: Re: [RFC PATCH] eventdev: ensure 16-byte alignment for events
Date: Fri, 6 Oct 2023 14:15:00 +0200 [thread overview]
Message-ID: <fcd11d73-d098-4734-9540-944aff73ed71@lysator.liu.se> (raw)
In-Reply-To: <20231005115101.12276-1-bruce.richardson@intel.com>
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>
> ---
> lib/eventdev/rte_eventdev.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/eventdev/rte_eventdev.h b/lib/eventdev/rte_eventdev.h
> index 2ba8a7b090..bb0d59b059 100644
> --- a/lib/eventdev/rte_eventdev.h
> +++ b/lib/eventdev/rte_eventdev.h
> @@ -1344,7 +1344,7 @@ struct rte_event {
> struct rte_event_vector *vec;
> /**< Event vector pointer. */
> };
> -};
> +} __rte_aligned(16);
>
> /* Ethdev Rx adapter capability bitmap flags */
> #define RTE_EVENT_ETH_RX_ADAPTER_CAP_INTERNAL_PORT 0x1
next prev parent reply other threads:[~2023-10-06 12:15 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 ` Mattias Rönnblom [this message]
2023-10-06 12:19 ` [RFC PATCH] " Bruce Richardson
2023-10-06 12:29 ` Mattias Rönnblom
2024-01-19 22:30 ` Stephen Hemminger
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