From 4097715c73ec48761c594b0807a8acd2c7a8f915 Mon Sep 17 00:00:00 2001 From: Keir Fraser Date: Tue, 18 Mar 2008 19:36:43 +0000 Subject: [PATCH] save/restore: Permute saved memory with 2MB chunk size. The memory permutation cause a slow down in case of a save/restore (bug 1143). It works better when the mixing is done with 2MB chunks. Signed-off-by: Jean Guyader --- tools/libxc/xc_domain_save.c | 30 +++++++++--------------------- 1 file changed, 9 insertions(+), 21 deletions(-) diff --git a/tools/libxc/xc_domain_save.c b/tools/libxc/xc_domain_save.c index 3bd2db08b6..fee353b7f9 100644 --- a/tools/libxc/xc_domain_save.c +++ b/tools/libxc/xc_domain_save.c @@ -125,34 +125,22 @@ static inline int count_bits ( int nr, volatile void *addr) return count; } -static inline int permute( int i, int nr, int order_nr ) +static inline int permute(unsigned long i, unsigned long order_nr) { /* Need a simple permutation function so that we scan pages in a pseudo random order, enabling us to get a better estimate of the domain's page dirtying rate as we go (there are often contiguous ranges of pfns that have similar behaviour, and we want to mix them up. */ + + unsigned char keep = 9; /* chunk of 2 MB */ + unsigned char shift_low = (order_nr - keep) / 2 + ((order_nr - keep) / 2) % 2; + unsigned char shift_high = order_nr - keep - shift_low; - /* e.g. nr->oder 15->4 16->4 17->5 */ - /* 512MB domain, 128k pages, order 17 */ + unsigned long high = (i >> (keep + shift_low)); + unsigned long low = (i >> keep) & ((1 << shift_low) - 1); - /* - QPONMLKJIHGFEDCBA - QPONMLKJIH - GFEDCBA - */ - - /* - QPONMLKJIHGFEDCBA - EDCBA - QPONM - LKJIHGF - */ - - do { i = ((i>>(order_nr-10)) | ( i<<10 ) ) & ((1<= nr ); /* this won't ever loop if nr is a power of 2 */ - - return i; + return (i & ((1 << keep) - 1)) | (low << (shift_high + keep)) | (high << keep); } static uint64_t tv_to_us(struct timeval *new) @@ -1126,7 +1114,7 @@ int xc_domain_save(int xc_handle, int io_fd, uint32_t dom, uint32_t max_iters, (batch < MAX_BATCH_SIZE) && (N < p2m_size); N++ ) { - int n = permute(N, p2m_size, order_nr); + int n = permute(N, order_nr); if ( debug ) { -- 2.30.2