Curl's detection of low-speed transfers creates a flood of timeout calls which significantly slows large transfers and increases CPU usage. This is fixed in https://github.com/curl/curl/commit/cacdc27f52 which is unfortunately not present on EL7.
This PR checks the curl version and only enables the low-speed detection when libcurl is new enough to have the fix.
Trying this patch on a production EL7 xrootd server which handles TPC requests, there was a significant drop in xrootd CPU usage: from ~100% busy, down to ~5%.
To see if the system is likely being affected, look for the function `Curl_speedcheck` appearing frequently in the gstack output for `xrootd`.
You can view, comment on, or merge this pull request online at:
https://github.com/xrootd/xrootd/pull/941
-- Commit Summary --
* [XrdTpc] Only use Curl's low-speed-limit with libcurl v7.38 and later
-- File Changes --
M src/XrdTpc/XrdTpcState.cc (13)
-- Patch Links --
https://github.com/xrootd/xrootd/pull/941.patch
https://github.com/xrootd/xrootd/pull/941.diff
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