INSTALL: Note about compiler atomics support.

OVS is slow when compiled with pthreads atomics. Add a generic note in INSTALL, with a reference to lib/ovs-atomic.h, where a new comment provides additional detail. Signed-off-by: Jarno Rajahalme <[email protected]>
subashd · Jun 4, 2014 · 29d204e · 29d204e
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diff --git a/INSTALL b/INSTALL
@@ -28,6 +28,10 @@ you will need the following software:
           analysis and thread-safety checks.  For Ubuntu, there are
           nightly built packages available on clang's website.
 
+      While OVS may be compatible with other compilers, optimal
+      support for atomic operations may be missing, making OVS very
+      slow (see lib/ovs-atomic.h).
+
     - libssl, from OpenSSL, is optional but recommended if you plan to
       connect the Open vSwitch to an OpenFlow controller.  libssl is
       required to establish confidentiality and authenticity in the

diff --git a/lib/ovs-atomic.h b/lib/ovs-atomic.h
@@ -257,6 +257,9 @@
     #elif HAVE_GCC4_ATOMICS
         #include "ovs-atomic-gcc4+.h"
     #else
+        /* ovs-atomic-pthreads implementation is provided for portability.
+         * It might be too slow for real use because Open vSwitch is
+         * optimized for platforms where real atomic ops are available. */
         #include "ovs-atomic-pthreads.h"
     #endif
 #undef IN_OVS_ATOMIC_H