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 <[EMAIL PROTECTED]> --- 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; - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
