Re: [PATCH] relay-file-read-start-pos-fix.patch

[David Wilder <dwilder@us.ibm.com>]

Ack
Works for me.  Thanks.

Note:
Both Masami's patch and the relay-file-read-start-pos-fix.patch I posted 
earlier are required.

Masami Hiramatsu wrote:

> Hi Tom,
>
> Tom Zanussi wrote:
>  
>
> > Could you send more info on how to reproduce the problem you're seeing?
> > And does this patch fix it?
> >    
>
> Sure, I'll explain how to reproduce it.
>
> Since current SystemTap is not supporting "overwrite" mode,
> you need to apply a patch before trying to reproduce it.
> I already posted the patch to bugzilla. You can get it from below.
> http://sourceware.org/bugzilla/attachment.cgi?id=1896&action=view
>
> Here is an example script (fillup.stp).
> ----
> global counter=0
> probe timer.ms(1) {
>        counter++;
>        printf("%08d : %020d\n", counter, gettimeofday_ns());
> }
> ----
>
> First of all, run the script with -O (overwrite mode) flag.
> (For simplify my explanation, I also use -m flag here.)
> $ stap -O fillup.stp -m fillup
> Soon after starting, press ^\(Ctrl+\) to detach from it.
>
> The script writes 32 bytes dummy data per 1 milli-second, so
> it writes about 32k bytes per 1 second.
> And the default size of relay channel of systemtap is 512kB
> which contains 4 subbufs (each size of subbufs is 128kB).
> Thus, it fills the relay channel at about 16 seconds and
> wraparounds because it uses overwrite mode.
>
> So, wait more than 16 seconds (for example, 18 sec),
> read the relay channel and count the line number.
> And repeat it.
> $ while true; do sleep 18; \
> cat /sys/kernel/debug/systemtap/fillup/trace0 | wc -l; done
>
> Ideally, it will show the number from 12288(=3*128k/32) to
> 16384(=4*128k/32).
>
> However, without my patch, it shows;
> 4793
> 5721
> 9818
> 9817
> 9819
> 13912
> 0
> 0
> 780
> 1625
> 5723
> 5721
>
> And, with my patch;
> 15742
> 13273
> 14901
> 12430
> 14056
> 15682
> 13215
> 14840
> 12370
> 13996
> 15624
> 13154
>
>
> So, I think my patch (which )fixes the problem.
>
> Thanks,
>
> P.S.
> I attached my patch (relay-file-read-overwrite-mode-fix.patch)
> which fixed the problem pointed in previous mail.
>
> Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
>
> ---
> kernel/relay.c |    8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> Index: linux-2.6.22-rc4-mm2/kernel/relay.c
> ===================================================================
> --- linux-2.6.22-rc4-mm2.orig/kernel/relay.c	2007-06-13 20:22:02.000000000 +0900
> +++ linux-2.6.22-rc4-mm2/kernel/relay.c	2007-06-20 10:53:06.000000000 +0900
> @@ -812,7 +812,10 @@
> 	}
>
> 	buf->bytes_consumed += bytes_consumed;
> -	read_subbuf = read_pos / buf->chan->subbuf_size;
> +	if (!read_pos)
> +		read_subbuf = buf->subbufs_consumed % n_subbufs;
> +	else
> +		read_subbuf = read_pos / buf->chan->subbuf_size;
> 	if (buf->bytes_consumed + buf->padding[read_subbuf] == subbuf_size) {
> 		if ((read_subbuf == buf->subbufs_produced % n_subbufs) &&
> 		    (buf->offset == subbuf_size))
> @@ -841,8 +844,9 @@
> 	}
>
> 	if (unlikely(produced - consumed >= n_subbufs)) {
> -		consumed = (produced / n_subbufs) * n_subbufs;
> +		consumed = produced - n_subbufs + 1;
> 		buf->subbufs_consumed = consumed;
> +		buf->bytes_consumed = 0;
> 	}
> 	
> 	produced = (produced % n_subbufs) * subbuf_size + buf->offset;
>
>
>
>
>
>  


--
David Wilder
IBM Linux Technology Center
Beaverton, Oregon, USA 
dwilder@us.ibm.com
(503)578-3789

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