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Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to refcount_t

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to refcount_t
Date 2017-03-22 18:00 +0100
Message-ID <tnRM6-5ys-27@gated-at.bofh.it> (permalink)
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On Wed, Mar 22, 2017 at 07:54:04AM -0700, Eric Dumazet wrote:
> 
> I guess someone could code a lib/test_refcount.c launching X threads
> using either atomic_inc or refcount_inc() in a loop.
> 
> That would give a rough estimate of the refcount_t overhead among
> various platforms.

Cycles spend on uncontended ops:

					SKL	SNB	IVB-EP

atomic:		lock incl		~15	~13	~10
atomic-ref:	call refcount_inc	~31	~37	~31
atomic-ref2:	$inlined		~23	~22	~21


Contended numbers (E3-1245 v5):


root@skl:~/spinlocks# LOCK=./atomic ./test1.sh
1: 14.797240
2: 87.451230
4: 100.747790
8: 118.234010

root@skl:~/spinlocks# LOCK=./atomic-ref ./test1.sh
1: 30.627320
2: 91.866730
4: 111.029560
8: 141.922420

root@skl:~/spinlocks# LOCK=./atomic-ref2 ./test1.sh
1: 23.243930
2: 98.620250
4: 119.604240
8: 124.864380



The code includes the patches found here:

  https://lkml.kernel.org/r/20170317211918.393791494@infradead.org

and effectively does:

#define REFCOUNT_WARN(cond, str) WARN_ON_ONCE(cond)

 s/WARN_ONCE/REFCOUNT_WARN/

on lib/refcount.c

Find the tarball of the userspace code used attached (its a bit of a
mess; its grown over time and needs a cleanup).

I used: gcc (Debian 6.3.0-6) 6.3.0 20170205


So while its about ~20 cycles worse, reducing contention is far more
effective than removing straight line instruction count (which too is
entirely possible, because GCC generates absolute shite in places).

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[PATCH 00/17] net subsystem refcount conversions Elena Reshetova <elena.reshetova@intel.com> - 2017-03-16 16:30 +0100
  [PATCH 02/17] net: convert neigh_params.refcnt from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-03-16 16:30 +0100
  [PATCH 10/17] net: convert in_device.refcnt from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-03-16 16:40 +0100
  [PATCH 12/17] net: convert unix_address.refcnt from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-03-16 16:40 +0100
  [PATCH 14/17] net: convert inet_frag_queue.refcnt from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-03-16 16:40 +0100
  [PATCH 01/17] net: convert neighbour.refcnt from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-03-16 16:40 +0100
  [PATCH 11/17] net: convert netpoll_info.refcnt from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-03-16 16:40 +0100
  [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-03-16 16:40 +0100
    Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Eric Dumazet <eric.dumazet@gmail.com> - 2017-03-16 18:00 +0100
      Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to refcount_t Kees Cook <keescook@chromium.org> - 2017-03-16 18:40 +0100
        Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t David Miller <davem@davemloft.net> - 2017-03-16 20:20 +0100
          RE: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2017-03-17 08:50 +0100
            Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Eric Dumazet <eric.dumazet@gmail.com> - 2017-03-17 17:20 +0100
              Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Herbert Xu <herbert@gondor.apana.org.au> - 2017-03-18 18:00 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t David Miller <davem@davemloft.net> - 2017-03-19 02:40 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Peter Zijlstra <peterz@infradead.org> - 2017-03-20 11:50 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Peter Zijlstra <peterz@infradead.org> - 2017-03-20 14:30 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Peter Zijlstra <peterz@infradead.org> - 2017-03-20 14:50 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Eric Dumazet <eric.dumazet@gmail.com> - 2017-03-20 16:00 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Eric Dumazet <eric.dumazet@gmail.com> - 2017-03-20 17:20 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Eric Dumazet <eric.dumazet@gmail.com> - 2017-03-20 17:40 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Eric Dumazet <eric.dumazet@gmail.com> - 2017-03-20 16:30 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Peter Zijlstra <peterz@infradead.org> - 2017-03-20 16:50 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to refcount_t Kees Cook <keescook@chromium.org> - 2017-03-21 21:50 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Eric Dumazet <eric.dumazet@gmail.com> - 2017-03-21 22:30 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t David Miller <davem@davemloft.net> - 2017-03-21 23:40 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to refcount_t Kees Cook <keescook@chromium.org> - 2017-03-22 01:00 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Eric Dumazet <eric.dumazet@gmail.com> - 2017-03-22 03:10 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Peter Zijlstra <peterz@infradead.org> - 2017-03-22 13:30 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Eric Dumazet <eric.dumazet@gmail.com> - 2017-03-22 14:30 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Peter Zijlstra <peterz@infradead.org> - 2017-03-22 15:40 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Eric Dumazet <eric.dumazet@gmail.com> - 2017-03-22 16:00 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Peter Zijlstra <peterz@infradead.org> - 2017-03-22 16:10 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Eric Dumazet <eric.dumazet@gmail.com> - 2017-03-22 16:30 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Peter Zijlstra <peterz@infradead.org> - 2017-03-22 18:00 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to refcount_t Kees Cook <keescook@chromium.org> - 2017-03-22 20:10 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Peter Zijlstra <peterz@infradead.org> - 2017-03-22 14:50 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Herbert Xu <herbert@gondor.apana.org.au> - 2017-03-20 15:50 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Herbert Xu <herbert@gondor.apana.org.au> - 2017-03-20 14:50 +0100
                RE: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t David Laight <David.Laight@ACULAB.COM> - 2017-03-20 15:20 +0100
                Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t Peter Zijlstra <peterz@infradead.org> - 2017-03-20 15:30 +0100
                RE: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to  refcount_t David Laight <David.Laight@ACULAB.COM> - 2017-03-20 16:10 +0100
  [PATCH 05/17] net: convert sk_buff_fclones.fclone_ref from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-03-16 16:40 +0100
  [PATCH 15/17] net: convert net.passive from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-03-16 16:40 +0100
  [PATCH 16/17] net: convert netlbl_lsm_cache.refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-03-16 16:40 +0100
  [PATCH 09/17] net: convert ip_mc_list.refcnt from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-03-16 16:40 +0100
  [PATCH 04/17] net: convert sk_buff.users from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-03-16 16:40 +0100
  [PATCH 08/17] net: convert sk_filter.refcnt from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-03-16 16:40 +0100
    Re: [PATCH 08/17] net: convert sk_filter.refcnt from atomic_t to  refcount_t Daniel Borkmann <daniel@iogearbox.net> - 2017-03-16 17:10 +0100
      RE: [PATCH 08/17] net: convert sk_filter.refcnt from atomic_t to  refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2017-03-17 09:20 +0100
  [PATCH 17/17] net: convert packet_fanout.sk_ref from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-03-16 16:40 +0100
  [PATCH 06/17] net: convert sock.sk_wmem_alloc from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-03-16 16:40 +0100
  [PATCH 13/17] net: convert fib_rule.refcnt from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-03-16 16:40 +0100

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