Messages in this thread | | | Date | Mon, 14 Sep 2015 13:27:01 -0500 (CDT) | From | Christoph Lameter <> | Subject | Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal due to a kernel NULL pointer dereference) |
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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.
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