On Sat, Mar 28, 2015 at 11:00 AM, Andy Walls <[email protected]> wrote:
> Hi, > > Can this memmove() be safely skipped > > > https://github.com/gnuradio/gnuradio/blob/master/gr-qtgui/lib/time_sink_f_impl.cc#L627 > > if ((d_start == 0) || (gr::high_res_timer_now() - d_last_time > > d_update_time))? > > I think it can, but I am not sure. > > With some high throughput, high sample rate flowgraphs, ps shows my > time_sink_f thread taking up ~41% of a CPU and oprofile shows memmove() > as the number 2 pig on the list: > > CPU: Intel Sandy Bridge microarchitecture, speed 3.5e+06 MHz (estimated) > Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit > mask of 0x00 (No unit mask) count 90000 > samples % image name symbol name > 24498 33.9825 libvolk.so.0.0.0 volk_32f_convert_64f_u_avx > 14278 19.8058 libc-2.18.so __memmove_ssse3_back > 7488 10.3870 no-vmlinux /no-vmlinux > 2668 3.7009 libgnuradio-qtgui-3.7.7git.so.0.0.0 > gr::qtgui::time_sink_f_impl::_test_trigger_slope(float const*) const > 2073 2.8756 libpthread-2.18.so pthread_mutex_lock > > The volk_32f_convert_64f_u_avx() call is unavoidable as Qwt wants > doubles for plotting and not floats. But it might also be able to be > deferred to the very end when the decision to plot is known for sure. > (But that's more surgery than I care to take on at the moment.) > > Regards, > Andy > The for loop there is in case we're triggering with a delay set, so that sets d_start into the buffers. But we pass the vector of buffers to the plotting widget, which will start at index 0. There are a couple of things that could work here. We add an argument to TimeUpdateEvent that adds the index value. We could also only do the memcpy if d_start > 0. But thinking about the volk convert function, that's both copying the data from the input buffer into the internal buffer as well as performing the conversion. We can't just hold data in the input since we don't want to back up the data until we're ready to plot both with timing and with a full enough buffer -- it's just sampling a section at a time and drops everything in between. That part could be converted into a memcpy instead of the volk convert. Then, when we're ready to plot, we call the volk convert that also does the move from d_start to 0, so it combines those two elements. Thoughts on those proposals? Tom
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