[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Re: how to avoid lost trace records?
Olaf, Dang, 8 megs per cpu -- but I guess that's really not so much overhead on a big machine; and it's definitely worth getting around the lost records issue. Send the T_INFO_PAGES patch to the list, and see what Keir thinks. There's probably a way to modify xenalyze to do start up gzip directly; may not be a bad idea. -George On Sat, Nov 20, 2010 at 8:21 PM, Olaf Hering <olaf@xxxxxxxxx> wrote: > On Fri, Nov 19, Olaf Hering wrote: > >> >> Today I inspected the xenalyze and the dump-raw output and noticed that >> huge number of lost trace records, even when booted with tbuf_size=200: >> >> grep -wn 1f001 log.sles11_6.xentrace.txt.dump-raw >> 274438:R p 5 o000000000063ffd4 1f001 4 t0000006d215b3c6b [ b6aed 57fff >> 9e668fb6 51 ] > ... >> That means more than 740K lost entries on cpu5,3,2,1,0. >> Is this expected? > > After reading the sources more carefully, its clear now. > There are a few constraints: > > If booted with tbuf_size=N, tracing starts right away and fills up the > buffer until xentrace collects its content. So entries will be lost. > > Once I just ran xentrace -e all > output, which filled up the whole disk > during my testing. So I changed the way to collect the output to a > compressed file: > > # mknod pipe p > # gzip -v9 < pipe > output.gz & > # xentrace -e all pipe & > > This means xentrace will stall until gzip has made room in the pipe. > Which also means xentrace cant collect more data from the tracebuffer > while waiting. So that is the reason for the lost entries. > > Now I changed T_INFO_PAGES in trace.c from 2 to 16, and reduced the > compression rate to speedup gzip emptying the pipe. > > # mknod pipe p > # nice -n -19 gzip -v1 < pipe > output.gz & > # nice -n -19 xentrace -s 1 -S 2031 -e $(( 0x10f000 )) pipe & > > > This means no more lost entries even with more than one guest running. > > > Olaf > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@xxxxxxxxxxxxxxxxxxx > http://lists.xensource.com/xen-devel > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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