Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932419AbbFQNPR (ORCPT ); Wed, 17 Jun 2015 09:15:17 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45271 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932318AbbFQNPM (ORCPT ); Wed, 17 Jun 2015 09:15:12 -0400 From: Igor Mammedov To: linux-kernel@vger.kernel.org Cc: mst@redhat.com, kvm@vger.kernel.org, pbonzini@redhat.com, andrey@xdel.ru, digitaleric@google.com Subject: [PATCH v2 5/6] vhost: add 'translation_cache' module parameter Date: Wed, 17 Jun 2015 15:14:58 +0200 Message-Id: <1434546899-5296-6-git-send-email-imammedo@redhat.com> In-Reply-To: <1434546899-5296-1-git-send-email-imammedo@redhat.com> References: <1434546899-5296-1-git-send-email-imammedo@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2424 Lines: 73 by default translation of virtqueue descriptors is done with caching enabled, but caching will add only extra cost in cases of trashing workload where majority descriptors are translated to different memory regions. So add an option to allow exclude cache miss cost for such cases. Performance with cashing enabled for sequential workload doesn't seem to be affected much vs version without static key switch, i.e. still the same 0.2% of total time with key(NOPs) consuming 5ms on 5min workload. Signed-off-by: Igor Mammedov --- I don't have a test case for trashing workload though, but jmp instruction adds up ~6ms(55M instructions) minus excluded caching around 24ms on 5min workload. --- drivers/vhost/vhost.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 5bcb323..78290b7 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -29,6 +29,13 @@ #include "vhost.h" +struct static_key translation_cache_key = STATIC_KEY_INIT_TRUE; +static bool translation_cache = true; +module_param(translation_cache, bool, 0444); +MODULE_PARM_DESC(translation_cache, + "Enables/disables virtqueue descriptor translation caching," + " Set to 0 to disable. (default: 1)"); + enum { VHOST_MEMORY_MAX_NREGIONS = 64, VHOST_MEMORY_F_LOG = 0x1, @@ -944,10 +951,12 @@ static const struct vhost_memory_region *find_region(struct vhost_memory *mem, const struct vhost_memory_region *reg; int start = 0, end = mem->nregions; - reg = mem->regions + *cached_reg; - if (likely(addr >= reg->guest_phys_addr && - reg->guest_phys_addr + reg->memory_size > addr)) - return reg; + if (static_key_true(&translation_cache_key)) { + reg = mem->regions + *cached_reg; + if (likely(addr >= reg->guest_phys_addr && + reg->guest_phys_addr + reg->memory_size > addr)) + return reg; + } while (start < end) { int slot = start + (end - start) / 2; @@ -1612,6 +1621,9 @@ EXPORT_SYMBOL_GPL(vhost_disable_notify); static int __init vhost_init(void) { + if (!translation_cache) + static_key_slow_dec(&translation_cache_key); + return 0; } -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/