On Mon, Mar 05, 2018 at 11:07:16AM -0800, Dave Hansen wrote: > On 03/05/2018 08:26 AM, Kirill A. Shutemov wrote: > > +void free_encrypt_page(struct page *page, int keyid, unsigned int order) > > +{ > > + int i; > > + void *v; > > + > > + for (i = 0; i < (1 << order); i++) { > > + v = kmap_atomic_keyid(page, keyid + i); > > + /* See comment in prep_encrypt_page() */ > > + clflush_cache_range(v, PAGE_SIZE); > > + kunmap_atomic(v); > > + } > > +} > > Have you measured how slow this is? Well, it's pretty bad. Tight loop of allocation/free a page (measured from within kernel) is 4-6 times slower: Encryption off Order-0, 10000000 iterations: 50496616 cycles Order-0, 10000000 iterations: 46900080 cycles Order-0, 10000000 iterations: 46873540 cycles Encryption on Order-0, 10000000 iterations: 222021882 cycles Order-0, 10000000 iterations: 222315381 cycles Order-0, 10000000 iterations: 222289110 cycles Encryption off Order-9, 100000 iterations: 46829632 cycles Order-9, 100000 iterations: 46919952 cycles Order-9, 100000 iterations: 37647873 cycles Encryption on Order-9, 100000 iterations: 222407715 cycles Order-9, 100000 iterations: 222111657 cycles Order-9, 100000 iterations: 222335352 cycles On macro benchmark it's not that dramatic, but still bad -- 16% down: Encryption off Performance counter stats for 'sh -c make -j100 -B -k >/dev/null' (5 runs): 6769369.623773 task-clock (msec) # 33.869 CPUs utilized ( +- 0.02% ) 1,086,729 context-switches # 0.161 K/sec ( +- 0.83% ) 193,153 cpu-migrations # 0.029 K/sec ( +- 0.72% ) 104,971,541 page-faults # 0.016 M/sec ( +- 0.01% ) 20,179,502,944,932 cycles # 2.981 GHz ( +- 0.02% ) 15,244,481,306,390 stalled-cycles-frontend # 75.54% frontend cycles idle ( +- 0.02% ) 11,548,852,154,412 instructions # 0.57 insn per cycle # 1.32 stalled cycles per insn ( +- 0.00% ) 2,488,836,449,779 branches # 367.661 M/sec ( +- 0.00% ) 94,445,965,563 branch-misses # 3.79% of all branches ( +- 0.01% ) 199.871815231 seconds time elapsed ( +- 0.17% ) Encryption on Performance counter stats for 'sh -c make -j100 -B -k >/dev/null' (5 runs): 8099514.432371 task-clock (msec) # 34.959 CPUs utilized ( +- 0.01% ) 1,169,589 context-switches # 0.144 K/sec ( +- 0.51% ) 198,008 cpu-migrations # 0.024 K/sec ( +- 0.77% ) 104,953,906 page-faults # 0.013 M/sec ( +- 0.01% ) 24,158,282,050,086 cycles # 2.983 GHz ( +- 0.01% ) 19,183,031,041,329 stalled-cycles-frontend # 79.41% frontend cycles idle ( +- 0.01% ) 11,600,772,560,767 instructions # 0.48 insn per cycle # 1.65 stalled cycles per insn ( +- 0.00% ) 2,501,453,131,164 branches # 308.840 M/sec ( +- 0.00% ) 94,566,437,048 branch-misses # 3.78% of all branches ( +- 0.01% ) 231.684539584 seconds time elapsed ( +- 0.15% ) I'll check what we can do here. -- Kirill A. Shutemov