Re: [Xen-devel] [PATCH v1] xen: make tracebuffer configurable

From: George Dunlap <George.Dunlap@citrix.com>
To: Baodong Chen <chenbaodong@mxnavi.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Wei Liu <wei.liu2@citrix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Andrew Cooper <Andrew.Cooper3@citrix.com>,
	"Tim \(Xen.org\)" <tim@xen.org>,
	George Dunlap <George.Dunlap@citrix.com>,
	Julien Grall <julien.grall@arm.com>,
	Jan Beulich <jbeulich@suse.com>,
	Ian Jackson <Ian.Jackson@citrix.com>,
	xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [Xen-devel] [PATCH v1] xen: make tracebuffer configurable
Date: Tue, 4 Jun 2019 10:49:38 +0000	[thread overview]
Message-ID: <B930162C-3D36-4182-9302-D0833A550C9C@citrix.com> (raw)
In-Reply-To: <1559609096-11356-1-git-send-email-chenbaodong@mxnavi.com>

> On Jun 4, 2019, at 1:44 AM, Baodong Chen <chenbaodong@mxnavi.com> wrote:
> 
> Xen internal running status(trace event) will be saved to
> trace memory when enabled. trace event data and config params can be
> read/changed by system control hypercall at run time.
> 
> Can be disabled for smaller code footprint.
> 
> Signed-off-by: Baodong Chen <chenbaodong@mxnavi.com>
> ---
> xen/common/Kconfig      | 12 ++++++++++++
> xen/common/Makefile     |  2 +-
> xen/include/xen/trace.h | 17 +++++++++++++++++
> 3 files changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/common/Kconfig b/xen/common/Kconfig
> index c838506..3459f56 100644
> --- a/xen/common/Kconfig
> +++ b/xen/common/Kconfig
> @@ -368,4 +368,16 @@ config DOM0_MEM
> 
> 	  Leave empty if you are not sure what to specify.
> 
> +config TRACEBUFFER
> +	bool "Enable trace event logs"  if EXPERT = "y"
> +	---help---
> +	  Xen internal running status(trace event) will be saved to trace memory
> +	  when enabled. trace event data and config params can be read/changed
> +	  by system control hypercall at run time.
> +
> +	  This is used to record xen internal running status.
> +	  with a litte performance overhead.
> +	  Can be set to 'N' if you dont want this function.
> +	  When not configured, 'XEN_STSCTL_tbuf_op' command will result 'ENOSYS’.

I think this would look better something like this:

“Enable tracing infrastructure”

“Enable in tracing infrastructure and pre-defined tracepoints within Xen.  This will allow live information about Xen’s execution and performance to be collected at run time for debugging or performance analysis.  Memory and execution overhead when not active is minimal."

Also, I’m not 100% familiar with the kconfig syntax — I think we want tracing enabled by default unless actively disabled; is that what will happen here?  Or will it only be enabled if EXPERT == ‘y’?

 -George

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