linux-kernel - Re: [PATCH 5/5] blktrace: print human-readable act

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Message-ID: <20090324083905.GB13016@elte.hu>
Date:	Tue, 24 Mar 2009 09:39:05 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Jens Axboe <jens.axboe@...cle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/5] blktrace: print human-readable act_mask

* Li Zefan <lizf@...fujitsu.com> wrote:

> Print stringified act_mask instead of hex value:
>  # cat act_mask
>  read,write,barrier,sync,queue,requeue,issue,complete,fs,pc,ahead,meta,
>  discard,drv_data
>  # echo "meta,write" > act_mask
>  # cat act_mask
>  write,meta

Nice!

It would also be nice to activate trace filters for the blktrace 
tracepoints - i.e. to convert them to the TRACE_EVENT() enumeration 
format. Beyond user-space parseable field enumeration and filter, 
that will also speed up tracing and allows binary record streaming 
with splice() zero-copy.

Via that "act_mask" can become a filterable field and you can define 
expressions to filter. All other fields like sector become in-kernel 
filterable too.

See a few examples here:

 include/trace/irq_event_types.h
 include/trace/sched_event_types.h

Note, blktrace tracepoints are certainly more complex than the 
tracepoints above - you can embedd C statements in TRACE_EVENT()'s 
TP_fast_assign() bit.

It was specifically designed to allow the support of blktrace 
tracepoints, so you can embedd the blk_pc_request() and disk_devt() 
translation for the block_rq_complete event or 
block_rq_requeue/issue tracepoints.

> +static struct {
> +	int mask;
> +	const char *str;
> +} mask_maps[] = {
> +	{ BLK_TC_READ,		"read"		},
> +	{ BLK_TC_WRITE,		"write"		},
> +	{ BLK_TC_BARRIER,	"barrier"	},
> +	{ BLK_TC_SYNC,		"sync"		},
> +	{ BLK_TC_QUEUE,		"queue"		},
> +	{ BLK_TC_REQUEUE,	"requeue"	},
> +	{ BLK_TC_ISSUE,		"issue"		},
> +	{ BLK_TC_COMPLETE,	"complete"	},
> +	{ BLK_TC_FS,		"fs"		},
> +	{ BLK_TC_PC,		"pc"		},
> +	{ BLK_TC_AHEAD,		"ahead"		},
> +	{ BLK_TC_META,		"meta"		},
> +	{ BLK_TC_DISCARD,	"discard"	},
> +	{ BLK_TC_DRV_DATA,	"drv_data"	},
> +};

(minor nit: this should be a const.)

Jens, Arnaldo, Steve, the series from Li looks good to me - Ack?

	Ingo
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