Am 28.02.2011 um 10:38 schrieb Stefan Hajnoczi:
Trace events outside the global mutex cannot be used with the simple
trace backend since it is not thread-safe. There is no check to
prevent
them being enabled so people sometimes learn this the hard way.
This patch restructures the simple trace backend with a ring buffer
suitable for multiple concurrent writers. A writeout thread
empties the
trace buffer when threshold fill levels are reached. Should the
writeout thread be unable to keep up with trace generation,
records will
simply be dropped.
Each time events are dropped a special record is written to the
trace
file indicating how many events were dropped. The event ID is
0xfffffffffffffffe and its signature is dropped(uint32_t count).
Signed-off-by: Stefan Hajnoczi <address@hidden>
---
v2:
* Add 'dropped' event so we know when events were lost.
[...]
+ __sync_synchronize(); /* read memory barrier before accessing
record
*/
Getting this at HEAD on Darwin/ppc64:
CC simpletrace.o
/Users/andreas/QEMU/qemu/simpletrace.c: In function
‘get_trace_record’:
/Users/andreas/QEMU/qemu/simpletrace.c:81: warning: implicit
declaration of
function ‘__sync_synchronize’
/Users/andreas/QEMU/qemu/simpletrace.c:81: warning: nested extern
declaration of ‘__sync_synchronize’
/Users/andreas/QEMU/qemu/simpletrace.c: In function ‘trace’:
/Users/andreas/QEMU/qemu/simpletrace.c:161: warning: implicit
declaration of
function ‘__sync_fetch_and_add’
/Users/andreas/QEMU/qemu/simpletrace.c:161: warning: nested extern
declaration of ‘__sync_fetch_and_add’
[...]
LINK qemu-nbd
Undefined symbols:
"___sync_fetch_and_add", referenced from:
_trace in simpletrace.o
"___sync_synchronize", referenced from:
_get_trace_record in simpletrace.o
_trace in simpletrace.o
ld: symbol(s) not found
collect2: ld returned 1 exit status
make: *** [qemu-nbd] Error 1
Haven't investigated further yet.