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authorStefan Hajnoczi <stefanha@linux.vnet.ibm.com>2011-02-26 18:38:39 +0000
committerStefan Hajnoczi <stefanha@linux.vnet.ibm.com>2011-03-07 15:34:17 +0000
commit0b5538c300a56c3cfb33022840fe0b4968147e7a (patch)
tree9b60b859d24881e2d032828c3788b2171f3ceaa6 /docs
parent07bf23a77131668ef8db37e08d508b117655ce86 (diff)
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simpletrace: Thread-safe tracing
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 <stefanha@linux.vnet.ibm.com>
Diffstat (limited to 'docs')
-rw-r--r--docs/tracing.txt5
1 files changed, 0 insertions, 5 deletions
diff --git a/docs/tracing.txt b/docs/tracing.txt
index a6cc56f..f15069c 100644
--- a/docs/tracing.txt
+++ b/docs/tracing.txt
@@ -141,11 +141,6 @@ source tree. It may not be as powerful as platform-specific or third-party
trace backends but it is portable. This is the recommended trace backend
unless you have specific needs for more advanced backends.
-Warning: the "simple" backend is not thread-safe so only enable trace events
-that are executed while the global mutex is held. Much of QEMU meets this
-requirement but some utility functions like qemu_malloc() or thread-related
-code cannot be safely traced using the "simple" backend.
-
==== Monitor commands ====
* info trace