Hi Daniel, On Thu, 18 Sep 2014, Daniel Stenberg wrote:
> On Thu, 18 Sep 2014, Pashupati Kumar wrote: > > > I am new to libcurI and still learning my ways around it. I have few > > questions on it. I discovered that user needs to copy the data in > > write call-back function and also the way our application behave, it > > will end up doing copy during read call back function as well. This > > will be a big draw-back as the application is data intensive. > > Will it really? Some people have claimed this over the years but I've never > seen > any real numbers proving this. On the contrary I think this is a common belief > and suspicion that rarely actually turns out to be an actual problem. > > Have you measured how much CPU - in your case - that would be "wasted" on > this extra copy? Or perhaps if that waste even makes a difference to the total > performance of your application. > I have not measured CPU required to perform copy operation. I understand that impact to application due to additional copy would depend on the nature of application. A telnet kind application wouldn't see impact whereas FTP probably would. To give you further background on the application. It needs to work with Cloud (private/public) object storage. So, here the comparison would be against protocols such as NFS (File) and iSCSI (Block), which is traditionally used for storage traffic. I came across this paper on memcpy performance. It tells me that a CORE running at 733 MHZ can do 400 MB per second. http://www.embedded.com/design/configurable-systems/4024961/Optimizing-Memcpy-improves-speed Please keep in mind that there would be another copy involved in Kernel ( from user data to Socket sk_buf). Are people using CURL library for storage traffic? If not, what is recommended library for doing so. > > I came across an old mail thread on avoiding copy for > CURLOPT_WRITEFUNCTION. > > I don't know what was the final outcome of it. > > We discuss this topic every once in a while and it always ends up getting > burried again when the work to implement something like this ends up being > more than the gains in having the feature. But maybe it is different this > time? > > > For read callback function, application data is available in scatter > > list of buffers. This brings me to my next question. Can libcurl use > > scatter-gather buffers? > > No. > Has this been considered before? Since Socket layer provide iovec based interface, will it be a huge change in the CURL library to expose it all the way to user? > -- > > / daniel.haxx.se > ------------------------------------------------------------------- > List admin: http://cool.haxx.se/list/listinfo/curl-library > Etiquette: http://curl.haxx.se/mail/etiquette.html ------------------------------------------------------------------- List admin: http://cool.haxx.se/list/listinfo/curl-library Etiquette: http://curl.haxx.se/mail/etiquette.html
