From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 14EAFC4338F for ; Fri, 30 Jul 2021 22:37:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E79CF60F42 for ; Fri, 30 Jul 2021 22:37:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232817AbhG3WhY (ORCPT ); Fri, 30 Jul 2021 18:37:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52446 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233310AbhG3WhX (ORCPT ); Fri, 30 Jul 2021 18:37:23 -0400 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AB801C06175F for ; Fri, 30 Jul 2021 15:37:17 -0700 (PDT) Received: by mail-yb1-xb49.google.com with SMTP id j9-20020a2581490000b02905897d81c63fso6553844ybm.8 for ; Fri, 30 Jul 2021 15:37:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=Fo9NvED0lpMkXN/JaIKCFquwO1thPwina4O0gbID30c=; b=Ayf8xXcekBEC/WtWhsL8b0fELKIo/kWYg2fpL1gfO/i1K1fxcCofieXaNyLbIv4zpq BmM4OVMuLdKosyOSvKtiXcYK2U8mkscxyMiANttRwiax8h0KX9/pc7l1hxfRV6CEBVwk 0IwRBzGz1b3Pjb5gC+rmzjmWV8pzix7HcOp5xRJ1KxJf/btpUiG03GNyXX6SCzONglJG dWQTu2DVrCzUPmDSt3MB4L1V0N7+BHfNxEmlVE6q3YK+tPDOaJAheQ1nxHvXmbEqc66A lvgGbUjNxCx2H00uFvDBSt5BXLXpEiSuRdJ/CYuJVoGAd+uOeBWnOm1o5+xcw+CHJeBP VYag== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=Fo9NvED0lpMkXN/JaIKCFquwO1thPwina4O0gbID30c=; b=o+sOXZDFDx+PPlzhwx8fcZ+N+1SGV3uG1FldcjDtamp9uMU8Cskba6uEoIdjMWVLVa BzcyXqSlZm9gwDc02wubWY91wECEX1J4wOg6Jk/m07OxCTRvQI8Y218+8Kt2YCOsyT0Q kOKezr8Bb7GCmkgODuGwW5XqWJyDTHb396s5aJJTRQg9MgE0iNJIyKKIz8TXWtGAc7rf x5vapovC3PK4ZAlAluAJjZG/ffdvIu2/CRgMgOSe/lRJY8x23krdmJHiTiXwOV9fJMnI POn/XtCbdvKzo8dNB6wvFqtt/bnMQhfDfhGeFP0qWlQkDOCG3H2iFIci3P7z/ak0P3q0 gvyQ== X-Gm-Message-State: AOAM532CrZundFM6/bbIhW8BuCbwW/NiDHP9re5+X2jpN+cJVu/seVTt EddKZPddsHtNO5P9S0UnXo+rs4TRuG/xLr2mJ0pMDmjqmcfYmjNFZvbqQfva67AknRqbaKI5HOc yFGBFzfd3UlbYLiG5NdDTRPQGayNAFJcCcMV8BFY9GZzbM7aLeIkXev4li0QNrRU= X-Google-Smtp-Source: ABdhPJwMnskhDblL6E8qFgZaYyvNXA8wYcJUVlWu79Mi0Q3msbXcQaS3Uf4RpviCGRUDy+BKatABfYafDH7KkQ== X-Received: from dmatlack-heavy.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:19cd]) (user=dmatlack job=sendgmr) by 2002:a25:b810:: with SMTP id v16mr6539371ybj.357.1627684636816; Fri, 30 Jul 2021 15:37:16 -0700 (PDT) Date: Fri, 30 Jul 2021 22:37:03 +0000 In-Reply-To: <20210730223707.4083785-1-dmatlack@google.com> Message-Id: <20210730223707.4083785-3-dmatlack@google.com> Mime-Version: 1.0 References: <20210730223707.4083785-1-dmatlack@google.com> X-Mailer: git-send-email 2.32.0.554.ge1b32706d8-goog Subject: [PATCH 2/6] KVM: Avoid VM-wide lru_slot lookup in kvm_vcpu_gfn_to_memslot From: David Matlack To: kvm@vger.kernel.org Cc: Ben Gardon , Joerg Roedel , Jim Mattson , Wanpeng Li , Vitaly Kuznetsov , Sean Christopherson , Paolo Bonzini , Junaid Shahid , Andrew Jones , David Matlack Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Now that vCPUs keep track of their own LRU slot, there's no good reason to have them check and update the VM-wide LRU slot. There's no performance data to motivate this change however there are two rationals: 1. Now that vCPUs have their own LRU slot, there's a potential for a double miss (miss the vCPU LRU slot and then miss the VM-wide LRU slot). By avoiding the VM-wide LRU slot check we keep the worst case to a single miss. 2. Large VMs are likely to have multiple memslots and vCPUs accessing different slots. Intuitively, vCPUs will end up thrashing the VM-wide LRU slot, decreasing the LRU hit rate for VM-wide operations such as mmu notifiers and VM ioctls. Signed-off-by: David Matlack --- include/linux/kvm_host.h | 20 +++++++++++--------- 1 file changed, 11 insertions(+), 9 deletions(-) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 320090d5a124..870e1e6fb771 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -1220,17 +1220,13 @@ static inline bool slot_contains_gfn(struct kvm_memslots *slots, int slot_index, static inline int __search_memslots(struct kvm_memslots *slots, gfn_t gfn) { int start = 0, end = slots->used_slots; - int slot = atomic_read(&slots->lru_slot); struct kvm_memory_slot *memslots = slots->memslots; if (unlikely(!slots->used_slots)) return -1; - if (slot_contains_gfn(slots, slot, gfn)) - return slot; - while (start < end) { - slot = start + (end - start) / 2; + int slot = start + (end - start) / 2; if (gfn >= memslots[slot].base_gfn) end = slot; @@ -1238,10 +1234,8 @@ static inline int __search_memslots(struct kvm_memslots *slots, gfn_t gfn) start = slot + 1; } - if (slot_contains_gfn(slots, start, gfn)) { - atomic_set(&slots->lru_slot, start); + if (slot_contains_gfn(slots, start, gfn)) return start; - } return -1; } @@ -1255,8 +1249,16 @@ static inline int __search_memslots(struct kvm_memslots *slots, gfn_t gfn) static inline struct kvm_memory_slot * search_memslots(struct kvm_memslots *slots, gfn_t gfn) { - int slot_index = __search_memslots(slots, gfn); + int slot_index = atomic_read(&slots->lru_slot); + + if (slot_contains_gfn(slots, slot_index, gfn)) + return get_slot(slots, slot_index); + + slot_index = __search_memslots(slots, gfn); + if (slot_index < 0) + return NULL; + atomic_set(&slots->lru_slot, slot_index); return get_slot(slots, slot_index); } -- 2.32.0.554.ge1b32706d8-goog