From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zachary Amsden Subject: Re: [PATCH 1/4] x86 paravirt_ops: create no_paravirt.h for native ops Date: Mon, 07 Aug 2006 13:51:50 -0700 Message-ID: <44D7A7E6.2060401@vmware.com> References: <1154925835.21647.29.camel@localhost.localdomain> <200608070730.17813.ak@muc.de> <1154930669.7642.12.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <1154930669.7642.12.camel@localhost.localdomain> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.osdl.org Errors-To: virtualization-bounces@lists.osdl.org To: Rusty Russell Cc: Andrew Morton , Andi Kleen , Linux Kernel Mailing List , Chris Wright , virtualization@lists.osdl.org List-Id: virtualization@lists.linuxfoundation.org Rusty Russell wrote: >>> + >>> +/* >>> + * Set IOPL bits in EFLAGS from given mask >>> + */ >>> +static inline void set_iopl_mask(unsigned mask) >>> = >> This function can be completely written in C using local_save_flags()/lo= cal_restore_flags() >> Please do that. I guess it's still a good idea to keep it separated >> though because it might allow other optimizations. >> >> e.g. i've been thinking about special casing IF changes in save/restore = flags = >> to optimize CPUs which have slow pushf/popf. If you already make sure >> all non IF manipulations of flags are separated that would help. >> = Actually, that is not quite true. Local_save_flags / = raw_local_irq_restore today is used only for operating on IF flag, and = raw_local_restore_flags does not exist. Our implementation of these in = VMI assumes that only the IF flag is being changed, and this is the = default assumption under which Xen runs as well. Using local_restore to = switch IOPL as well causes the extremely performance critical common = case of pure IRQ restore to do potentially a lot more work in a hypervisor. So if you do want us to go with the C approach, I would propose using = raw_local_iopl_restore, which can make a different hypercall (actually, = in our case, this is not even a hypercall, merely a VMI call). Zach