Bug 1779060

Summary:	gmp is compiled without CPU optimizations enabled
Product:	[Fedora] Fedora	Reporter:	Nikos Mavrogiannopoulos <nmavrogi>
Component:	gmp	Assignee:	Jakub Martisko <jamartis>
Status:	CLOSED RAWHIDE	QA Contact:	Fedora Extras Quality Assurance <extras-qa>
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	rawhide	CC:	deekej, frantisek.kluknavsky, jamartis, ssorce
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Last Closed:	2019-12-03 09:40:10 UTC	Type:	---
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Bug Blocks:	1779057

Description Nikos Mavrogiannopoulos 2019-12-03 07:53:41 UTC

This bug was initially created as a copy of Bug #1779057

I am copying this bug because: 



Description of problem:
In an unrelated fedora commit 2b62e65299c881127f59855ac54eb999b55afc34 the --enable-fat flag which was enabling CPU optimized code was dropped, probably accidentally. That's has a significant impact on the performance of nettle and in turn gnutls.

In particular the RSA implementation of nettle as compared to openssl drops to (hogweed-benchmark tool):
            name size   sign/ms verify/ms
            rsa 2048    0.8881   27.1422
  rsa (openssl) 2048    1.4249   45.2295


While on a non-Fedora system where gmp is compiled with --enable-fat:
             rsa 2048    0.2106    7.2703
   rsa (openssl) 2048    0.2024    6.4992

Please compile gmp with --enable-fat

Comment 1 Nikos Mavrogiannopoulos 2019-12-03 08:04:23 UTC

https://src.fedoraproject.org/rpms/gmp/pull-request/2

Comment 2 Jakub Martisko 2019-12-03 09:40:10 UTC

Should be fixed in rawhide: https://koji.fedoraproject.org/koji/taskinfo?taskID=39420536

Comment 3 Nikos Mavrogiannopoulos 2019-12-03 10:41:33 UTC

Did you measure any significant benefit? On my x86-64 if I compile the same source code locally I get:

             rsa 2048    1.5079   53.4444
   rsa (openssl) 2048    1.8138   61.0715


while, the fedora code after the --enable-fat is significantly slower:
             rsa 2048    1.1020   41.3436
   rsa (openssl) 2048    1.8138   61.0715


You can verify the benchmark by compiling https://gitlab.com/gnutls/nettle and running
$ examples/hogweed-test rsa

Comment 4 Jakub Martisko 2019-12-03 12:00:53 UTC

I've tried the benchmark with the original version, the rawhide version and [1] (this should be the last version before the --enable-fat was removed) and I'm getting:

rsa 2048    1.2620   45.5201
rsa 2048    1.1557   43.8995
rsa 2048    1.1458   43.8338

respectively

[1]: https://koji.fedoraproject.org/koji/buildinfo?buildID=843681

Comment 5 Jakub Martisko 2019-12-03 12:03:19 UTC

The values are from running examples/hogweed-benchmark from the gitlab repo from comment#3

Comment 6 Nikos Mavrogiannopoulos 2019-12-03 13:22:59 UTC

When compiling locally I see that the flags used by gmp are:
-mtune=skylake  -march=broadwell -fomit-frame-pointer

while fedora sets: -mtune=generic

Adding -fomit-frame-pointer does not give much, so it seems that the mtune and march give a very big boost in my case. Not sure what we can do to take advantage of that :(

Comment 7 Simo Sorce 2019-12-03 13:58:08 UTC

Nikos, we should consult with someone in glibc/dev tool on techniques to enable different code paths on different architectures.
I know it is possible to do at runtime (like enabling AVX2 when available and falling back to SSSE3 when not and similar), but it may require significant engineering around GMP to do that.