| Message ID | 20200625184838.28172-2-philmd@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | block/nvme: Various cleanups required to use multiple queues | expand |
On Thu, Jun 25, 2020 at 08:48:22PM +0200, Philippe Mathieu-Daudé wrote: > Avoid further processing if TRACE_NVME_SUBMIT_COMMAND_RAW is > not enabled. Why? This saves 8 trace events, each with 8 arguments. I guess the intent is to improve performance. Did you measure an improvement?
On 6/26/20 12:36 PM, Stefan Hajnoczi wrote: > On Thu, Jun 25, 2020 at 08:48:22PM +0200, Philippe Mathieu-Daudé wrote: >> Avoid further processing if TRACE_NVME_SUBMIT_COMMAND_RAW is >> not enabled. > > Why? > > This saves 8 trace events, each with 8 arguments. I guess the intent is > to improve performance. Did you measure an improvement? No testing, I just tried to outsmart the compiler :/
On Fri, Jun 26, 2020 at 04:02:43PM +0200, Philippe Mathieu-Daudé wrote: > On 6/26/20 12:36 PM, Stefan Hajnoczi wrote: > > On Thu, Jun 25, 2020 at 08:48:22PM +0200, Philippe Mathieu-Daudé wrote: > >> Avoid further processing if TRACE_NVME_SUBMIT_COMMAND_RAW is > >> not enabled. > > > > Why? > > > > This saves 8 trace events, each with 8 arguments. I guess the intent is > > to improve performance. Did you measure an improvement? > > No testing, I just tried to outsmart the compiler :/ Usually performance patches are accompanied with benchmark results. Otherwise it's easy to modify code without making a difference or accidentally introducing performance regressions. But this is a small change and I'm not worried. Please do explicitly state in the commit description that this is intended as a performance optimization. I wasn't exactly sure about the reason for this change. Stefan
diff --git a/block/nvme.c b/block/nvme.c index eb2f54dd9d..1e5b40f61c 100644 --- a/block/nvme.c +++ b/block/nvme.c @@ -367,6 +367,9 @@ static void nvme_trace_command(const NvmeCmd *cmd) { int i; + if (!trace_event_get_state_backends(TRACE_NVME_SUBMIT_COMMAND_RAW)) { + return; + } for (i = 0; i < 8; ++i) { uint8_t *cmdp = (uint8_t *)cmd + i * 8; trace_nvme_submit_command_raw(cmdp[0], cmdp[1], cmdp[2], cmdp[3],
Avoid further processing if TRACE_NVME_SUBMIT_COMMAND_RAW is not enabled. Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com> --- block/nvme.c | 3 +++ 1 file changed, 3 insertions(+)