The environment is: Ubuntu 14.04 64bit with the most recent kernel C-Library: glibc 2.19 Compiler: GCC 4.8.2 All available updates of Ubuntu have been installed. I was surprised myself. My first thought was, you call it to often, but that's not the case. read() and send() are cheap, because they would use DMA if available. The memcpy implementation used is __memcpy_sse2_unaligned, I really have no idea, why this is so slow. Valgrind should not be a problem, the generated output should not contain instructions from the tool and it should not modify anything from a normal program run. And the CPU load and bad transfer rates even occure without it. I tested the file example again with -O3 and no -g, performance is far better (No surprise here), but still worse than the patched version. Transfer rates are good, but CPU load is about 20% lower with the patch. I will do a new comparison with Valgrind next week. Btw: In your examples Makefile you set -g in line 1 and again in line 16.
Am Donnerstag, 25. September 2014 10:39:04 UTC+2 schrieb Sergey Lyubka: > > Thanks Marcel. > > I am really (mean, really) surprised to see that memcpy() call was a > bottleneck. > Are we sure that valgrind instrumentation doesn't interfere here? > > Could you elaborate more on you environment please - OS, C library, > compiler, etc? > If you build with full optimization on, do you see the same CPU load? > > > On Thu, Sep 25, 2014 at 8:09 AM, Marcel Wirtz <[email protected] > <javascript:>> wrote: > >> Thanks Sergey, >> >> the patch works great so far. I tested the file example with your patch >> applied and, as predicted, the CPU instruction count went down by about >> 60%. CPU load as shown by top also decreased by about the same factor and >> download speed has increased, especially with multiple parallel downloads. >> 2 parallel downloads have the same total transfer rate as a single >> download, without the patch it decreased rapidly, limited by the CPU usage. >> >> An analysis with callgrind now shows FD_* macros as the biggest impact on >> CPU load, and i don't think, there's a way to save anything there. >> >> >> Am Freitag, 19. September 2014 23:57:17 UTC+2 schrieb Sergey Lyubka: >>> >>> Thanks Macel. >>> Could you try on attached patch please? >>> >>> >>> >>> On Thu, Sep 18, 2014 at 12:19 PM, Marcel Wirtz <[email protected]> wrote: >>> >>>> The problem is definetly not IO related (And no other software I know >>>> has such a high CPU load transferring data from a file to a socket). >>>> >>>> A short analysis of the problem: >>>> >>>> in transfer_file_data() read is called to read data from the file to a >>>> buffer (0.29% of the total CPU instructions). Then ns_send() is called. >>>> Here the buffer is copied to another buffer (59.27% CPU instructions in >>>> memcpy). send() is called by ns_write_to_socket() and uses 0.49% of the >>>> CPU >>>> instructions. So the real problem is not reading from the file or writing >>>> to the socket, but the internal copy of the buffer in ns_send(). If there >>>> would be a way not to copy every byte of the file internaly before >>>> sending, >>>> the CPU load should be smaller (about 60%, which would be better by far). >>>> >>>> Am Mittwoch, 17. September 2014 09:54:11 UTC+2 schrieb Sergey Lyubka: >>>>> >>>>> Well if that is memcpy, then I don't find it surprising. >>>>> Server is mostly doing data copying, reading from file and copying to >>>>> the socket. >>>>> >>>>> >>>>> >>>>> On Sat, Sep 13, 2014 at 12:11 PM, Marcel Wirtz <[email protected]> >>>>> wrote: >>>>> >>>>>> Yes >>>>>> >>>>>> -- >>>>>> You received this message because you are subscribed to the Google >>>>>> Groups "mongoose-users" group. >>>>>> To unsubscribe from this group and stop receiving emails from it, >>>>>> send an email to [email protected]. >>>>>> To post to this group, send email to [email protected]. >>>>>> Visit this group at http://groups.google.com/group/mongoose-users. >>>>>> For more options, visit https://groups.google.com/d/optout. >>>>>> >>>>> >>>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "mongoose-users" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to [email protected]. >>>> To post to this group, send email to [email protected]. >>>> Visit this group at http://groups.google.com/group/mongoose-users. >>>> For more options, visit https://groups.google.com/d/optout. >>>> >>> >>> -- >> You received this message because you are subscribed to the Google Groups >> "mongoose-users" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected] <javascript:>. >> To post to this group, send email to [email protected] >> <javascript:>. >> Visit this group at http://groups.google.com/group/mongoose-users. >> For more options, visit https://groups.google.com/d/optout. >> > > -- You received this message because you are subscribed to the Google Groups "mongoose-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/mongoose-users. For more options, visit https://groups.google.com/d/optout.
