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Message-ID: <7f494c4ae5a041fbafa4059e85431857@amazon.com>
Date: Thu, 31 Oct 2024 18:28:19 +0000
From: "Kiyanovski, Arthur" <akiyano@...zon.com>
To: Caleb Sander Mateos <csander@...estorage.com>, Andrew Lunn
	<andrew+netdev@...n.ch>, AngeloGioacchino Del Regno
	<angelogioacchino.delregno@...labora.com>, Brett Creeley
	<brett.creeley@....com>, Broadcom internal kernel review list
	<bcm-kernel-feedback-list@...adcom.com>, Christophe Leroy
	<christophe.leroy@...roup.eu>, Claudiu Manoil <claudiu.manoil@....com>,
	"Arinzon, David" <darinzon@...zon.com>, "David S. Miller"
	<davem@...emloft.net>, Doug Berger <opendmb@...il.com>, Eric Dumazet
	<edumazet@...gle.com>, Eugenio PĂ©rez
	<eperezma@...hat.com>, Felix Fietkau <nbd@....name>, Florian Fainelli
	<florian.fainelli@...adcom.com>, Geetha sowjanya <gakula@...vell.com>,
	hariprasad <hkelam@...vell.com>, Jakub Kicinski <kuba@...nel.org>, Jason Wang
	<jasowang@...hat.com>, Jonathan Corbet <corbet@....net>, Leon Romanovsky
	<leon@...nel.org>, Lorenzo Bianconi <lorenzo@...nel.org>, Louis Peens
	<louis.peens@...igine.com>, Mark Lee <Mark-MC.Lee@...iatek.com>, "Matthias
 Brugger" <matthias.bgg@...il.com>, Michael Chan <michael.chan@...adcom.com>,
	"Michael S. Tsirkin" <mst@...hat.com>, "Dagan, Noam" <ndagan@...zon.com>,
	Paolo Abeni <pabeni@...hat.com>, Przemek Kitszel
	<przemyslaw.kitszel@...el.com>, Roy Pledge <Roy.Pledge@....com>, "Bshara,
 Saeed" <saeedb@...zon.com>, Saeed Mahameed <saeedm@...dia.com>, Sean Wang
	<sean.wang@...iatek.com>, Shannon Nelson <shannon.nelson@....com>, "Agroskin,
 Shay" <shayagr@...zon.com>, Simon Horman <horms@...nel.org>, "Subbaraya
 Sundeep" <sbhatta@...vell.com>, Sunil Goutham <sgoutham@...vell.com>, "Tal
 Gilboa" <talgi@...dia.com>, Tariq Toukan <tariqt@...dia.com>, Tony Nguyen
	<anthony.l.nguyen@...el.com>, Vladimir Oltean <vladimir.oltean@....com>, Xuan
 Zhuo <xuanzhuo@...ux.alibaba.com>
CC: "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-doc@...r.kernel.org"
	<linux-doc@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-mediatek@...ts.infradead.org"
	<linux-mediatek@...ts.infradead.org>, "linuxppc-dev@...ts.ozlabs.org"
	<linuxppc-dev@...ts.ozlabs.org>, "linux-rdma@...r.kernel.org"
	<linux-rdma@...r.kernel.org>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, "oss-drivers@...igine.com"
	<oss-drivers@...igine.com>, "virtualization@...ts.linux.dev"
	<virtualization@...ts.linux.dev>
Subject: RE: [resend PATCH 2/2] dim: pass dim_sample to net_dim() by reference

> -----Original Message-----
> From: Caleb Sander Mateos <csander@...estorage.com>
> Sent: Wednesday, October 30, 2024 5:23 PM
> 
> net_dim() is currently passed a struct dim_sample argument by value.
> struct dim_sample is 24 bytes. Since this is greater 16 bytes, x86-64 passes it
> on the stack. All callers have already initialized dim_sample on the stack, so
> passing it by value requires pushing a duplicated copy to the stack. Either
> witing to the stack and immediately reading it, or perhaps dereferencing
> addresses relative to the stack pointer in a chain of push instructions, seems
> to perform quite poorly.
> 
> In a heavy TCP workload, mlx5e_handle_rx_dim() consumes 3% of CPU time,
> 94% of which is attributed to the first push instruction to copy dim_sample on
> the stack for the call to net_dim():
> // Call ktime_get()
>   0.26 |4ead2:   call   4ead7 <mlx5e_handle_rx_dim+0x47>
> // Pass the address of struct dim in %rdi
>        |4ead7:   lea    0x3d0(%rbx),%rdi
> // Set dim_sample.pkt_ctr
>        |4eade:   mov    %r13d,0x8(%rsp)
> // Set dim_sample.byte_ctr
>        |4eae3:   mov    %r12d,0xc(%rsp)
> // Set dim_sample.event_ctr
>   0.15 |4eae8:   mov    %bp,0x10(%rsp)
> // Duplicate dim_sample on the stack
>  94.16 |4eaed:   push   0x10(%rsp)
>   2.79 |4eaf1:   push   0x10(%rsp)
>   0.07 |4eaf5:   push   %rax
> // Call net_dim()
>   0.21 |4eaf6:   call   4eafb <mlx5e_handle_rx_dim+0x6b>
> 
> To allow the caller to reuse the struct dim_sample already on the stack, pass
> the struct dim_sample by reference to net_dim().
> 
> Signed-off-by: Caleb Sander Mateos <csander@...estorage.com>
> ---

Thank you for this patch.

For the ENA part:

Reviewed-by: Arthur Kiyanovski <akiyano@...zon.com>

Thanks,
Arthur

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