From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756883AbbFPQfN (ORCPT ); Tue, 16 Jun 2015 12:35:13 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49636 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756462AbbFPQdo (ORCPT ); Tue, 16 Jun 2015 12:33:44 -0400 From: Igor Mammedov To: linux-kernel@vger.kernel.org Cc: mst@redhat.com, kvm@vger.kernel.org, pbonzini@redhat.com Subject: [PATCH 1/5] vhost: use binary search instead of linear in find_region() Date: Tue, 16 Jun 2015 18:33:35 +0200 Message-Id: <1434472419-148742-2-git-send-email-imammedo@redhat.com> In-Reply-To: <1434472419-148742-1-git-send-email-imammedo@redhat.com> References: <1434472419-148742-1-git-send-email-imammedo@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org For default region layouts performance stays the same as linear search i.e. it takes around 210ns average for translate_desc() that inlines find_region(). But it scales better with larger amount of regions, 235ns BS vs 300ns LS with 55 memory regions and it will be about the same values when allowed number of slots is increased to 509 like it has been done in kvm. Signed-off-by: Igor Mammedov --- drivers/vhost/vhost.c | 38 ++++++++++++++++++++++++++++---------- 1 file changed, 28 insertions(+), 10 deletions(-) diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 2ee2826..a22f8c3 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -25,6 +25,7 @@ #include #include #include +#include #include "vhost.h" @@ -590,6 +591,16 @@ int vhost_vq_access_ok(struct vhost_virtqueue *vq) } EXPORT_SYMBOL_GPL(vhost_vq_access_ok); +static int vhost_memory_reg_sort_cmp(const void *p1, const void *p2) +{ + const struct vhost_memory_region *r1 = p1, *r2 = p2; + if (r1->guest_phys_addr < r2->guest_phys_addr) + return 1; + if (r1->guest_phys_addr > r2->guest_phys_addr) + return -1; + return 0; +} + static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m) { struct vhost_memory mem, *newmem, *oldmem; @@ -609,9 +620,11 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m) memcpy(newmem, &mem, size); if (copy_from_user(newmem->regions, m->regions, mem.nregions * sizeof *m->regions)) { - kfree(newmem); + kvfree(newmem); return -EFAULT; } + sort(newmem->regions, newmem->nregions, sizeof(*newmem->regions), + vhost_memory_reg_sort_cmp, NULL); if (!memory_access_ok(d, newmem, 0)) { kfree(newmem); @@ -913,17 +926,22 @@ EXPORT_SYMBOL_GPL(vhost_dev_ioctl); static const struct vhost_memory_region *find_region(struct vhost_memory *mem, __u64 addr, __u32 len) { - struct vhost_memory_region *reg; - int i; + const struct vhost_memory_region *reg; + int start = 0, end = mem->nregions; - /* linear search is not brilliant, but we really have on the order of 6 - * regions in practice */ - for (i = 0; i < mem->nregions; ++i) { - reg = mem->regions + i; - if (reg->guest_phys_addr <= addr && - reg->guest_phys_addr + reg->memory_size - 1 >= addr) - return reg; + while (start < end) { + int slot = start + (end - start) / 2; + reg = mem->regions + slot; + if (addr >= reg->guest_phys_addr) + end = slot; + else + start = slot + 1; } + + reg = mem->regions + start; + if (addr >= reg->guest_phys_addr && + reg->guest_phys_addr + reg->memory_size > addr) + return reg; return NULL; } -- 1.8.3.1