Hallo, Egon Alter wrote:
> I did some measurements compiling the openSUSE kernel: Thanks! > git clean, dropped caches > > no ccache: 5391.75user 639.29system 31:26.27elapsed 319%CPU > with ccache: 887.53user 289.11system 15:07.42elapsed 129%CPU > with ccache + cow: 933.62user 318.38system 18:56.00elapsed 110%CPU > > So surprisingly, ccache + cow is slower than without cow. Uh oh. > I can only guess > that the compilation is IO limited in both cases and that using reflink > instead of copy doesn't reduce it significantly for some reason (many small > files maybe?). The filesystem was using compression (lzo) btw. Hrm... btrfs's compression can sometimes interfere with other features like (no)cow, so I gave in and ran some quick & dirty tests. Set-up: compiling ccache with itself seemed fitting, finishes in finite time on an old netbook, and produces a handful of nice >4 KiB object files that can't be inlined. Result: unless 'filefrag -v' is lying or btrfs silently ignores a 'remount,compress={none,lzo}' (and mind you: both are always possible with a fledgling file system), CoW works flawlessly here in both cases, and in both directions. Not a single extent is duplicated once the initial object file has been compiled. Oh: and it's consistently slower. Bah. T G-R _______________________________________________ ccache mailing list ccache@lists.samba.org https://lists.samba.org/mailman/listinfo/ccache