Re: [Qemu-devel] [PATCH 3/4] trace: Clean up the "try to update atomic until it worked" loops

[Harsh Bora]

On 01/25/2013 09:13 PM, Markus Armbruster wrote:
> Signed-off-by: Markus Armbruster <address@hidden>
> ---
>   trace/simple.c | 18 +++++-------------
>   1 file changed, 5 insertions(+), 13 deletions(-)

Reviewed-by: Harsh Prateek Bora <address@hidden>

> diff --git a/trace/simple.c b/trace/simple.c
> index 592ff48..74701e3 100644
> --- a/trace/simple.c
> +++ b/trace/simple.c
> @@ -171,13 +171,10 @@ static gpointer writeout_thread(gpointer opaque)
>               dropped.rec.timestamp_ns = get_clock();
>               dropped.rec.length = sizeof(TraceRecord) + sizeof(uint64_t),
>               dropped.rec.reserved = 0;
> -            while (1) {
> +            do {
>                   dropped_count = g_atomic_int_get(&dropped_events);
> -                if (g_atomic_int_compare_and_exchange(&dropped_events,
> -                                                      dropped_count, 0)) {
> -                    break;
> -                }
> -            }
> +            } while (!g_atomic_int_compare_and_exchange(&dropped_events,
> +                                                        dropped_count, 0));
>               dropped.rec.arguments[0] = dropped_count;
>               unused = fwrite(&dropped.rec, dropped.rec.length, 1, trace_fp);
>           }
> @@ -213,7 +210,7 @@ int trace_record_start(TraceBufferRecord *rec, TraceEventID 
> event, size_t datasi
>       uint32_t rec_len = sizeof(TraceRecord) + datasize;
>       uint64_t timestamp_ns = get_clock();
>
> -    while (1) {
> +    do {
>           old_idx = g_atomic_int_get(&trace_idx);
>           smp_rmb();
>           new_idx = old_idx + rec_len;
> @@ -223,12 +220,7 @@ int trace_record_start(TraceBufferRecord *rec, 
> TraceEventID event, size_t datasi
>               g_atomic_int_inc(&dropped_events);
>               return -ENOSPC;
>           }
> -
> -        if (g_atomic_int_compare_and_exchange(&trace_idx,
> -                                              old_idx, new_idx)) {
> -            break;
> -        }
> -    }
> +    } while (!g_atomic_int_compare_and_exchange(&trace_idx, old_idx, new_idx));
>
>       idx = old_idx % TRACE_BUF_LEN;