[ovs-dev] [PATCH v3] Improved Packet Drop Statistics in OVS
Ben Pfaff
blp at ovn.org
Mon Sep 10 19:50:58 UTC 2018
On Mon, Sep 10, 2018 at 11:07:08AM +0000, Keshav Gupta wrote:
> Hi Ben
> I am not quite getting the below error. I believe this may be coming because of existing macro atomic_read_explicit definition.
> #define atomic_read_explicit(SRC, DST, ORDER) \
> (*(DST) = atomic_load_explicit(SRC, ORDER), \
> (void) 0)
> Where I believe it is cribbing for (void)0 which gcc is cribbing that it may not have any effect. I have corrected the other errors.
>
> I see some discussion of this sort in this URL. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61081
> From the discussion if I understood correctly it is a false alarm present from gcc 4.9.
>
>
> >> In file included from ../lib/ovs-atomic.h:331,
> >> from ../lib/dpif-netdev-perf.h:32,
> >> from ../lib/dpif-netdev-perf.c:20:
> >> ../lib/dpif-netdev-perf.c: In function 'pmd_perf_drop_stats_clear':
> >> ../lib/ovs-atomic-c11.h:31:47: error: right-hand operand of comma expression has no effect [-Werror=unused-value]
> >> (*(DST) = atomic_load_explicit(SRC, ORDER), \
> >> ^
> >> ../lib/ovs-atomic.h:401:5: note: in expansion of macro 'atomic_read_explicit'
> >> atomic_read_explicit(VAR, DST, memory_order_relaxed)
> >> ^~~~~~~~~~~~~~~~~~~~
> >> ../lib/dpif-netdev-perf.c:474:9: note: in expansion of macro 'atomic_read_relaxed'
> >> atomic_read_relaxed(&s->drop_counters.n.rx_drops[i],
> >> ^~~~~~~~~~~~~~~~~~~
> >> ../lib/ovs-atomic-c11.h:31:47: error: right-hand operand of comma expression has no effect [-Werror=unused-value]
> (*(DST) = atomic_load_explicit(SRC, ORDER), \
One problem I see is that you're trying to use atomic_read_relaxed() to
store into an atomic variable. It's only for reading one, not writing
to one. Try fixing that.
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