From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=50868 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Pg0Wk-0002Lc-R8 for qemu-devel@nongnu.org; Thu, 20 Jan 2011 14:50:39 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Pg0Wj-0005to-CF for qemu-devel@nongnu.org; Thu, 20 Jan 2011 14:50:38 -0500 Received: from mail-qy0-f173.google.com ([209.85.216.173]:58715) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Pg0Wj-0005tf-7D for qemu-devel@nongnu.org; Thu, 20 Jan 2011 14:50:37 -0500 Received: by qyl38 with SMTP id 38so2298584qyl.4 for ; Thu, 20 Jan 2011 11:50:36 -0800 (PST) Message-ID: <4D389209.8070202@codemonkey.ws> Date: Thu, 20 Jan 2011 13:50:33 -0600 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] [RFC PATCH] Fake machine for scalability testing References: <4D38642C.5050306@codemonkey.ws> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Markus Armbruster Cc: qemu-devel@nongnu.org On 01/20/2011 11:12 AM, Markus Armbruster wrote: > Anthony Liguori writes: > > >> On 01/18/2011 02:16 PM, Markus Armbruster wrote: >> >>> The problem: you want to do serious scalability testing (1000s of VMs) >>> of your management stack. If each guest eats up a few 100MiB and >>> competes for CPU, that requires a serious host machine. Which you don't >>> have. You also don't want to modify the management stack at all, if you >>> can help it. >>> >>> The solution: a perfectly normal-looking QEMU that uses minimal >>> resources. Ability to execute any guest code is strictly optional ;) >>> >>> New option -fake-machine creates a fake machine incapable of running >>> guest code. Completely compiled out by default, enable with configure >>> --enable-fake-machine. >>> >>> With -fake-machine, CPU use is negligible, and memory use is rather >>> modest. >>> >>> Non-fake VM running F-14 live, right after boot: >>> UID PID PPID C SZ RSS PSR STIME TTY TIME CMD >>> armbru 15707 2558 53 191837 414388 1 21:05 pts/3 00:00:29 [...] >>> >>> Same VM -fake-machine, after similar time elapsed: >>> UID PID PPID C SZ RSS PSR STIME TTY TIME CMD >>> armbru 15742 2558 0 85129 9412 0 21:07 pts/3 00:00:00 [...] >>> >>> We're using a very similar patch for RHEL scalability testing. >>> >>> >> Interesting, but: >> >> 9432 anthony 20 0 153m 14m 5384 S 0 0.2 0:00.22 >> qemu-system-x86 >> >> That's qemu-system-x86 -m 4 >> > Sure you ran qemu-system-x86 -fake-machine? > No, I didn't try it. My point was that -m 4 is already pretty small. >> In terms of memory overhead, the largest source is not really going to >> be addressed by -fake-machine (l1_phys_map and phys_ram_dirty). >> > git-grep phys_ram_dirty finds nothing. > Yeah, it's now ram_list[i].phys_dirty. l1_phys_map is (sizeof(void *) + sizeof(PhysPageDesc)) * mem_size_in_pages phys_dirty is mem_size_in_pages bytes. >> I don't really understand the point of not creating a VCPU with KVM. >> Is there some type of overhead in doing that? >> > I briefly looked at both main loops, TCG's was the first one I happened > to crack, and I didn't feel like doing both then. If the general > approach is okay, I'll gladly investigate how to do it with KVM. > I guess what I don't understand is why do you need to not run guest code? Specifically, if you remove the following, is it any less useful? diff --git a/cpu-exec.c b/cpu-exec.c index 8c9fb8b..cd1259a 100644 --- a/cpu-exec.c +++ b/cpu-exec.c @@ -230,7 +230,7 @@ int cpu_exec(CPUState *env1) uint8_t *tc_ptr; unsigned long next_tb; - if (cpu_halted(env1) == EXCP_HALTED) + if (fake_machine || cpu_halted(env1) == EXCP_HALTED) return EXCP_HALTED; Regards, Anthony Liguori