On Wed, May 18, 2011 at 10:00:12AM -0700, Tim Bird wrote: > On 05/18/2011 12:54 AM, Christoph Hellwig wrote: > > On Tue, May 17, 2011 at 04:33:07PM -0700, Tim Bird wrote: > >> That said, I can answer Greg's question. This is to speed up > >> the symbol resolution on module loading. The last numbers I > >> saw showed a reduction of about 15-20% for the module load > >> time, for large-ish modules. Of course this is highly dependent > >> on the size of the modules, what they do at load time, and how many > >> symbols are looked up to link them into the kernel. > > > > How large are these very large modules, and what are good examples for > > that? > > usbcore seems to be a large-ish module whose > load time is improved by this. More details follow: Then add the module to the kernel image, that's what a lot of distros do now to solve this issue. > I don't know the exact modules, but Alan Jenkins reported a .3 > second reduction in overall boot time, on a EEE PC, presumably > running a stock Linux distribution, and loading 41 modules. > > See http://lkml.org/lkml/2009/11/3/93 That's good to know. > Carmelo Amoroso reported some good performance gains > in this presentation: > http://elinux.org/images/1/18/C_AMOROSO_Fast_lkm_loader_ELC-E_2009.pdf > (See slide 22). > > He doesn't report the overall time savings, and > he was using a different method (hash tables as opposed to > binary search), but I believe the results are comparable > to what the binary search enhancement provides. > > The biggest offenders in his testing were usbcore, > ehci_hcd and ohci_hcd. Why those? The size of them, or something else? They don't seem to have very many symbols they need to look up compared to anything else that I can tell. Is something else going on here due to the serialization of the USB drivers themselves? > > And why do people overly care for the load time? > > To reduce overall boot time. To reduce it even more, build the modules into the kernel :) I'm not saying I object to this patch, I just want a whole lot more information in it when submitted as currently there was no justification for the change at all. thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
