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From: Alexander Aring <aahringo@redhat.com>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: linux-trace-devel@vger.kernel.org, linux-trace-users@vger.kernel.org
Subject: Re: RFC: using NIC DMA ring as tracing buffer?
Date: Wed, 17 Apr 2024 18:51:26 -0400	[thread overview]
Message-ID: <CAK-6q+h=5LcjtTxJ0i3BcaVZRGfyWpQJy6Htxjh_zFfOgUpwfA@mail.gmail.com> (raw)
In-Reply-To: <46859f90-bdf6-4502-bf6a-4add6dad3668@efficios.com>

Hi Mathieu,

On Tue, Apr 16, 2024 at 10:49 AM Mathieu Desnoyers
<mathieu.desnoyers@efficios.com> wrote:
>
> On 2024-04-16 10:41, Alexander Aring wrote:
> > Hi all,
> >
> > I have an idea about using the DMA rings of a networking card as a
> > tracing buffer.
>
> The first thing I'd be worried about is overhead caused by
> false-sharing if you trace a large SMP/many-core system all
> into the same global NIC buffer. The cache lines will bounce
> left and right which is bad performance-wise.
>

modern NICs have several tx and rx dma rings. There is an ethtool
command to query the number:

sudo ethtool -g $IFACE

so it depends on the hardware if you can pin one or more rings on a
per-cpu buffer basis.

I hope that somehow helps to make this idea less worrisome.

Thanks.

- Alex


  reply	other threads:[~2024-04-17 22:51 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-04-16 14:41 RFC: using NIC DMA ring as tracing buffer? Alexander Aring
2024-04-16 14:48 ` Mathieu Desnoyers
2024-04-17 22:51   ` Alexander Aring [this message]
2024-04-17 23:05     ` Alexander Aring

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