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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 E72E9C0650F for ; Mon, 5 Aug 2019 11:56:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C6178206A2 for ; Mon, 5 Aug 2019 11:56:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728695AbfHEL4j (ORCPT ); Mon, 5 Aug 2019 07:56:39 -0400 Received: from mail-wr1-f66.google.com ([209.85.221.66]:37508 "EHLO mail-wr1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728681AbfHEL4h (ORCPT ); Mon, 5 Aug 2019 07:56:37 -0400 Received: by mail-wr1-f66.google.com with SMTP id n9so59051308wrr.4 for ; Mon, 05 Aug 2019 04:56:36 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:openpgp:message-id :date:user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=TY4SwjXmEN9gc5bLylSn4Hg0/dB7NKueAsPGd6xGBoQ=; b=QB/BSZwdzuDkotLcFHtMEhOnmdWeZoV95B8M+SQMDirOTrzFWg6e8TJYUAGZh62Nld vG6BW3ehzIDr76Zq4QD7IXMA8PxsU81riK7ixXdm4ALLyZ8f5dnMPK9WQI7MnA3OOt+i M8SqsWH9i9rwzBCA8PYp9bL90gRdsPlX8/RQd1JYk23rNG87BriVKUK97MoUDLd3eDz4 N4qshsk2Pr0C9gFLSJjY0Y9eg69UGZFgWd0l/dlqYvE1etBo21sZKE1LybCS/YVhdv2e q0cJW0OVTQ7ra6t/2JUVUX9uzk4W9R3I5tEEijMMB0f2mOfqFaL/WUMs2CfZU5+BTTJk XdFA== X-Gm-Message-State: APjAAAUhpLnzXfsxi9z/xHSY66R2/7ZvHO3sCrvOmpUpXqDAg7pLnToi 9jHYkNSuDxpiRn8mmSYYPdyvrJTxK3k= X-Google-Smtp-Source: APXvYqyiW6VU1XQOFEG2eUsh/f6zKNWC3klkjjD7J05dOiekrtpHuIxq6IVPBKdC0E3ZEqXFzkJjhg== X-Received: by 2002:a5d:4cc5:: with SMTP id c5mr107334032wrt.278.1565006195708; Mon, 05 Aug 2019 04:56:35 -0700 (PDT) Received: from [192.168.178.40] ([151.21.165.91]) by smtp.gmail.com with ESMTPSA id v15sm77198646wrt.25.2019.08.05.04.56.34 (version=TLS1_3 cipher=AEAD-AES128-GCM-SHA256 bits=128/128); Mon, 05 Aug 2019 04:56:35 -0700 (PDT) Subject: Re: [RFC PATCH v2 07/19] RISC-V: KVM: Implement KVM_GET_ONE_REG/KVM_SET_ONE_REG ioctls To: Christian Borntraeger , Anup Patel , Palmer Dabbelt , Paul Walmsley , Radim K Cc: Daniel Lezcano , Thomas Gleixner , Atish Patra , Alistair Francis , Damien Le Moal , Christoph Hellwig , Anup Patel , "kvm@vger.kernel.org" , "linux-riscv@lists.infradead.org" , "linux-kernel@vger.kernel.org" References: <20190802074620.115029-1-anup.patel@wdc.com> <20190802074620.115029-8-anup.patel@wdc.com> From: Paolo Bonzini Openpgp: preference=signencrypt Message-ID: <8563b869-1ab4-d0f1-afad-9cd864b6019a@redhat.com> Date: Mon, 5 Aug 2019 13:56:34 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/08/19 13:37, Christian Borntraeger wrote: > While have ONE_REG will certainly work, have you considered the sync_reg scheme > (registers as part of kvm_run structure) > This will speed up the exit to QEMU as you do not have to do multiple ioctls > (each imposing a systemcall overhead) for one exit. > > Ideally you should not exit too often into qemu, but for those cases sync_regs > is faster than ONE_REG. At least in theory, RISC-V should never have exits to QEMU that need accessing the registers. (The same is true for x86; Google implemented sync_regs because they moved the instruction emulator to userspace in their fork). Paolo