mirror of
https://git.FreeBSD.org/src.git
synced 2024-12-20 11:11:24 +00:00
ddab052725
Clang emits SSE instructions on amd64 in the common path of pthread_mutex_unlock. If the thread does not otherwise use SSE, this usage incurs a context-switch of the FPU/SSE state, which reduces the performance of multiple real-world applications by a non-trivial amount (3-5% in one application). Instead of this change, I experimented with eagerly switching the FPU state at context-switch time. This did not help. Most of the cost seems to be in the read/write of memory--as kib@ stated--and not in the #NM handling. I tested on machines with and without XSAVEOPT. One counter-argument to this change is that most applications already use SIMD, and the number of applications and amount of SIMD usage are only increasing. This is absolutely true. I agree that--in general and in principle--this change is in the wrong direction. However, there are applications that do not use enough SSE to offset the extra context-switch cost. SSE does not provide a clear benefit in the current libthr code with the current compiler, but it does provide a clear loss in some cases. Therefore, disabling SSE in libthr is a non-loss for most, and a gain for some. I refrained from disabling SSE in libc--as was suggested--because I can't make the above argument for libc. It provides a wide variety of code; each case should be analyzed separately. https://lists.freebsd.org/pipermail/freebsd-current/2015-March/055193.html Suggestions from: dim, jmg, rpaulo Approved by: kib (mentor) MFC after: 2 weeks Sponsored by: Dell Inc. |
||
|---|---|---|
| .. | ||
| atf | ||
| atrun | ||
| bootpd | ||
| casper | ||
| comsat | ||
| dma | ||
| dma-mbox-create | ||
| fingerd | ||
| ftpd | ||
| getty | ||
| hyperv | ||
| mail.local | ||
| mknetid | ||
| pppoed | ||
| rbootd | ||
| revnetgroup | ||
| rlogind | ||
| rpc.rquotad | ||
| rpc.rstatd | ||
| rpc.rusersd | ||
| rpc.rwalld | ||
| rpc.sprayd | ||
| rshd | ||
| rtld-aout | ||
| rtld-elf | ||
| save-entropy | ||
| smrsh | ||
| talkd | ||
| tcpd | ||
| telnetd | ||
| tests | ||
| tftp-proxy | ||
| tftpd | ||
| ulog-helper | ||
| ypxfr | ||
| Makefile | ||
| Makefile.amd64 | ||
| Makefile.i386 | ||
| Makefile.inc | ||
| Makefile.pc98 | ||