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Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by walking all the percpu data at once

From Eric Dumazet <eric.dumazet@gmail.com>
Newsgroups linux.kernel
Subject Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by walking all the percpu data at once
Date 2015-08-29 00:30 +0200
Message-ID <q2AjL-89a-5@gated-at.bofh.it> (permalink)
References (6 earlier) <q2yUF-60W-3@gated-at.bofh.it> <q2yUF-60W-1@gated-at.bofh.it> <q2z4m-6rs-11@gated-at.bofh.it> <q2ze2-6CP-11@gated-at.bofh.it> <q2znJ-6NW-23@gated-at.bofh.it>
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On Fri, 2015-08-28 at 14:26 -0700, Joe Perches wrote:

> Always a possibility, but I don't think so.
> 
> > put_unaligned is happening on a space allocated from rtnetlink skb, not
> > the temp space needed to perform the per cpu folding.
> 
> That's why I suggested changing the snmp_fill_stats arguments.
> 
> If the naturally aligned allocated u64 array is used and then
> copied as a block to the rtnetlink skb, I believe there's no
> alignment issue that would require put_unaligned.

1) u64 array[XX] on stack is naturally aligned,
kzalloc() wont improve this at all. Not sure what you believe.

2) put_unaligned() is basically a normal memory write on x86.
 memcpy(dst,src,...) will have a problem anyway on arches that care,
because src & dst wont have same alignment.

288 bytes on stack in a leaf function in this path is totally fine, it
is not like we're calling ext4/xfs/nfs code after this point.


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[PATCH RFC V2 0/2]  Optimize the snmp stat aggregation for large cpus  Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> - 2015-08-26 19:50 +0200
  [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by walking all the percpu data at once Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> - 2015-08-26 19:50 +0200
    Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by  walking all the percpu data at once David Miller <davem@davemloft.net> - 2015-08-27 20:40 +0200
      Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by walking  all the percpu data at once Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> - 2015-08-28 08:40 +0200
        Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by  walking all the percpu data at once David Miller <davem@davemloft.net> - 2015-08-28 20:30 +0200
          Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by  walking all the percpu data at once Joe Perches <joe@perches.com> - 2015-08-28 21:30 +0200
            Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by  walking all the percpu data at once Eric Dumazet <eric.dumazet@gmail.com> - 2015-08-28 22:40 +0200
              Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by  walking all the percpu data at once Eric Dumazet <eric.dumazet@gmail.com> - 2015-08-28 23:00 +0200
                Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by  walking all the percpu data at once Joe Perches <joe@perches.com> - 2015-08-28 23:10 +0200
                Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by  walking all the percpu data at once Eric Dumazet <eric.dumazet@gmail.com> - 2015-08-28 23:20 +0200
                Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by  walking all the percpu data at once Joe Perches <joe@perches.com> - 2015-08-28 23:30 +0200
                Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by  walking all the percpu data at once Eric Dumazet <eric.dumazet@gmail.com> - 2015-08-29 00:30 +0200
                Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by  walking all the percpu data at once Joe Perches <joe@perches.com> - 2015-08-29 01:20 +0200
                Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by  walking all the percpu data at once Eric Dumazet <eric.dumazet@gmail.com> - 2015-08-29 02:10 +0200
                Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by  walking all the percpu data at once Joe Perches <joe@perches.com> - 2015-08-29 02:40 +0200
                Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by  walking all the percpu data at once Eric Dumazet <eric.dumazet@gmail.com> - 2015-08-29 03:10 +0200
              Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by  walking all the percpu data at once Joe Perches <joe@perches.com> - 2015-08-28 23:00 +0200
          Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by  walking all the percpu data at once Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> - 2015-08-29 05:00 +0200
            Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by  walking all the percpu data at once Eric Dumazet <eric.dumazet@gmail.com> - 2015-08-29 05:30 +0200
              Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by walking  all the percpu data at once Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> - 2015-08-29 10:00 +0200
            Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by  walking all the percpu data at once David Miller <davem@davemloft.net> - 2015-08-29 07:20 +0200
              Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by walking  all the percpu data at once Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> - 2015-08-29 10:00 +0200

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