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Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal due to a kernel NULL pointer dereference)

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On 2015-09-14 14:27, Christoph Lameter wrote:
> On Mon, 14 Sep 2015, Austin S Hemmelgarn wrote:
>
>> I can comment at least a little about the -Os aspect (although not I'm no
>> expert on this in particular).  In general, for _most_ use cases, a
>> kernel
>> compiled with CONFIG_CC_OPTIMIZE_FOR_SIZE will run slower than one
>> compiled
>> without it.  On rare occasion though, it may actually run faster, the
>> only
>> cases I've seen where this happens are specialized uses that are very
>> memory
>> pressure dependent and run almost entirely in userspace with almost no
>> syscalls (for example math related stuff operating on _very, very big_
>> (as in,
>> >1 trillion elements) multidimensional matrices, with complex memory
>> constraints), and even then it's usually a miniscule improvement in
>> performance (generally less than 1%, which can of course be significant
>> depending on how long it takes before the improvement).
>
> Cache footprint depends on size which has a significant impact on
> performance. In our experience the kernel (and any other code) is
> generally faster if optimized for size.
>
Ah, yes, there is that too (like I tried to say, and messed up my 
grammar in doing so, I'm no expert), although on processors that 
actually have a reasonable amount of cache, this is not usually 
something most people would notice without a benchmark except on a very 
slow processor (HPC workloads and gamers notwithstanding of course).

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Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal  due to a kernel NULL pointer dereference) Baoquan He <bhe@redhat.com> - 2015-09-09 04:40 +0200
  Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal due  to a kernel NULL pointer dereference) Sedat Dilek <sedat.dilek@gmail.com> - 2015-09-09 05:00 +0200
    Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal due  to a kernel NULL pointer dereference) Sedat Dilek <sedat.dilek@gmail.com> - 2015-09-09 05:20 +0200
    Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal  due to a kernel NULL pointer dereference) Baoquan He <bhe@redhat.com> - 2015-09-09 05:30 +0200
      Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal due  to a kernel NULL pointer dereference) Sedat Dilek <sedat.dilek@gmail.com> - 2015-09-09 05:50 +0200
        Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal  due to a kernel NULL pointer dereference) Peter Zijlstra <peterz@infradead.org> - 2015-09-09 15:00 +0200
          Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal due  to a kernel NULL pointer dereference) Sedat Dilek <sedat.dilek@gmail.com> - 2015-09-12 23:30 +0200
            Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal  due to a kernel NULL pointer dereference) Peter Zijlstra <peterz@infradead.org> - 2015-09-14 09:20 +0200
              Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal due  to a kernel NULL pointer dereference) Sedat Dilek <sedat.dilek@gmail.com> - 2015-09-14 09:40 +0200
                Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal due  to a kernel NULL pointer dereference) Sedat Dilek <sedat.dilek@gmail.com> - 2015-09-14 10:00 +0200
                Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal  due to a kernel NULL pointer dereference) Peter Zijlstra <peterz@infradead.org> - 2015-09-14 11:00 +0200
                Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal  due to a kernel NULL pointer dereference) Ingo Molnar <mingo@kernel.org> - 2015-09-14 11:40 +0200
                Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal  due to a kernel NULL pointer dereference) Ingo Molnar <mingo@kernel.org> - 2015-09-14 12:00 +0200
                Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal due  to a kernel NULL pointer dereference) Sedat Dilek <sedat.dilek@gmail.com> - 2015-09-14 12:30 +0200
                Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal  due to a kernel NULL pointer dereference) Ingo Molnar <mingo@kernel.org> - 2015-09-14 14:50 +0200
                Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal due  to a kernel NULL pointer dereference) Sedat Dilek <sedat.dilek@gmail.com> - 2015-09-14 12:00 +0200
              Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal due  to a kernel NULL pointer dereference) Sedat Dilek <sedat.dilek@gmail.com> - 2015-09-14 09:50 +0200
                Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal due  to a kernel NULL pointer dereference) Austin S Hemmelgarn <ahferroin7@gmail.com> - 2015-09-14 20:00 +0200
                Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal  due to a kernel NULL pointer dereference) Christoph Lameter <cl@linux.com> - 2015-09-14 20:30 +0200
                Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal due  to a kernel NULL pointer dereference) Austin S Hemmelgarn <ahferroin7@gmail.com> - 2015-09-14 20:40 +0200
                Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal  due to a kernel NULL pointer dereference) Ingo Molnar <mingo@kernel.org> - 2015-09-15 08:20 +0200

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