On 2015-09-14 14:27, Christoph Lameter wrote:
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).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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