> From: Minchan Kim [mailto:minchan@xxxxxxxxxx] > Subject: Re: [PATCH 3/3] x86: add local_tlb_flush_kernel_range() > > Hello, > > On 06/27/2012 03:14 PM, Alex Shi wrote: > > > On 06/27/2012 01:53 PM, Minchan Kim wrote: > > > >> On 06/26/2012 01:14 AM, Seth Jennings wrote: > >> > >>> This patch adds support for a local_tlb_flush_kernel_range() > >>> function for the x86 arch. This function allows for CPU-local > >>> TLB flushing, potentially using invlpg for single entry flushing, > >>> using an arch independent function name. > >>> > >>> Signed-off-by: Seth Jennings <sjenning@xxxxxxxxxxxxxxxxxx> > >> > >> > >> Anyway, we don't matter INVLPG_BREAK_EVEN_PAGES's optimization point is 8 or something. > > > > > > Different CPU type has different balance point on the invlpg replacing > > flush all. and some CPU never get benefit from invlpg, So, it's better > > to use different value for different CPU, not a fixed > > INVLPG_BREAK_EVEN_PAGES. > > I think it could be another patch as further step and someone who are > very familiar with architecture could do better than. > So I hope it could be merged if it doesn't have real big problem. > > Thanks for the comment, Alex. Just my opinion, but I have to agree with Alex. Hardcoding behavior that is VERY processor-specific is a bad idea. TLBs should only be messed with when absolutely necessary, not for the convenience of defending an abstraction that is nice-to-have but, in current OS kernel code, unnecessary. IIUC, zsmalloc only cares that the breakeven point is greater than two. An arch-specific choice of (A) two page flushes vs (B) one all-TLB flush should be all that is necessary right now. (And, per separate discussion, even this isn't really necessary either.) If zsmalloc _ever_ gets extended to support items that might span three or more pages, a more generic TLB flush-pages-vs-flush-all approach may be warranted and, by then, may already exist in some future kernel. Until then, IMHO, keep it simple. _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/devel
