linux-kernel - Re: [PATCH 08/15] tracing: Introduce names for ring buffers

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Date:   Tue, 12 Dec 2023 19:44:41 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alexander Graf <graf@...zon.com>
Cc:     <linux-kernel@...r.kernel.org>,
        <linux-trace-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <kexec@...ts.infradead.org>, <linux-doc@...r.kernel.org>,
        <x86@...nel.org>, Eric Biederman <ebiederm@...ssion.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Rob Herring <robh+dt@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mark Rutland <mark.rutland@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Ashish Kalra <ashish.kalra@....com>,
        James Gowans <jgowans@...zon.com>,
        "Stanislav Kinsburskii" <skinsburskii@...ux.microsoft.com>,
        <arnd@...db.de>, <pbonzini@...hat.com>,
        <madvenka@...ux.microsoft.com>,
        Anthony Yznaga <anthony.yznaga@...cle.com>,
        Usama Arif <usama.arif@...edance.com>,
        "David Woodhouse" <dwmw@...zon.co.uk>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 08/15] tracing: Introduce names for ring buffers

On Wed, 13 Dec 2023 01:35:16 +0100
Alexander Graf <graf@...zon.com> wrote:

> > The trace_array is the structure that represents each tracing instance. And
> > it already has a name field. And if you can get the associated ring buffer
> > from that too.
> >
> > struct trace_array *tr;
> >
> >          tr->array_buffer.buffer
> >
> >          tr->name
> >
> > When you do: mkdir /sys/kernel/tracing/instance/foo
> >
> > You create a new trace_array instance where tr->name = "foo" and allocates
> > the buffer for it as well.  
> 
> The name in the ring buffer is pretty much just a copy of the trace 
> array name. I use it to reconstruct which buffer we're actually 
> referring to inside __ring_buffer_alloc().

No, I rather not tie the ring buffer to the trace_array.

> 
> I'm all ears for alternative suggestions. I suppose we could pass tr as 
> argument to ring_buffer_alloc() instead of the name?

I'll have to spend some time (that I don't currently have :-( ) on looking
at this more. I really don't like the copying of the name into the ring
buffer allocation, as it may be an unneeded burden to maintain, not to
mention the duplicate field.

-- Steve