From: Dave Hansen <dave.hansen@intel.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>,
"seanjc@google.com" <seanjc@google.com>
Cc: "Gao, Chao" <chao.gao@intel.com>,
"Yamahata, Isaku" <isaku.yamahata@intel.com>,
"x86@kernel.org" <x86@kernel.org>,
"kas@kernel.org" <kas@kernel.org>, "bp@alien8.de" <bp@alien8.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"Zhao, Yan Y" <yan.y.zhao@intel.com>,
"Huang, Kai" <kai.huang@intel.com>,
"mingo@redhat.com" <mingo@redhat.com>,
"pbonzini@redhat.com" <pbonzini@redhat.com>,
"linux-coco@lists.linux.dev" <linux-coco@lists.linux.dev>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>
Subject: Re: [PATCHv2 00/12] TDX: Enable Dynamic PAMT
Date: Wed, 13 Aug 2025 16:31:29 -0700 [thread overview]
Message-ID: <d21a66fe-d2ce-46cc-b89e-b60b03eae3da@intel.com> (raw)
In-Reply-To: <f38f55de6f4d454d0288eb7f04c8c621fb7b9508.camel@intel.com>
On 8/13/25 15:43, Edgecombe, Rick P wrote:
> I redid the test. Boot 10 TDs with 16GB of ram, run userspace to fault in memory
> from 4 threads until OOM, then shutdown. TDs were split between two sockets. It
> ended up with 1136 contentions of the global lock, 4ms waiting.
4ms out of how much CPU time?
Also, contention is *NOT* necessarily bad here. Only _false_ contention.
The whole point of the lock is to ensure that there aren't two different
CPUs trying to do two different things to the same PAMT range at the
same time.
If there are, one of them *HAS* to wait. It can wait lots of different
ways, but it has to wait. That wait will show up as spinlock contention.
Even if the global lock went away, that 4ms of spinning might still be
there.
next prev parent reply other threads:[~2025-08-13 23:31 UTC|newest]
Thread overview: 90+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-06-09 19:13 [PATCHv2 00/12] TDX: Enable Dynamic PAMT Kirill A. Shutemov
2025-06-09 19:13 ` [PATCHv2 01/12] x86/tdx: Consolidate TDX error handling Kirill A. Shutemov
2025-06-25 17:58 ` Dave Hansen
2025-06-25 20:58 ` Edgecombe, Rick P
2025-06-25 21:27 ` Sean Christopherson
2025-06-25 21:46 ` Edgecombe, Rick P
2025-06-26 9:25 ` kirill.shutemov
2025-06-26 14:46 ` Dave Hansen
2025-06-26 15:51 ` Sean Christopherson
2025-06-26 16:59 ` Dave Hansen
2025-06-27 10:42 ` kirill.shutemov
2025-07-30 18:32 ` Edgecombe, Rick P
2025-07-31 23:31 ` Sean Christopherson
2025-07-31 23:46 ` Edgecombe, Rick P
2025-07-31 23:53 ` Sean Christopherson
2025-08-01 15:03 ` Edgecombe, Rick P
2025-08-06 15:19 ` Sean Christopherson
2025-06-26 0:05 ` Huang, Kai
2025-07-30 18:33 ` Edgecombe, Rick P
2025-06-09 19:13 ` [PATCHv2 02/12] x86/virt/tdx: Allocate page bitmap for Dynamic PAMT Kirill A. Shutemov
2025-06-25 18:06 ` Dave Hansen
2025-06-26 9:25 ` Kirill A. Shutemov
2025-07-31 1:06 ` Edgecombe, Rick P
2025-07-31 4:10 ` Huang, Kai
2025-06-26 11:08 ` Huang, Kai
2025-06-27 10:42 ` kirill.shutemov
2025-06-09 19:13 ` [PATCHv2 03/12] x86/virt/tdx: Allocate reference counters for PAMT memory Kirill A. Shutemov
2025-06-25 19:26 ` Dave Hansen
2025-06-27 11:27 ` Kirill A. Shutemov
2025-06-27 14:03 ` Dave Hansen
2025-06-26 0:53 ` Huang, Kai
2025-06-26 4:48 ` Huang, Kai
2025-06-27 11:35 ` kirill.shutemov
2025-06-09 19:13 ` [PATCHv2 04/12] x86/virt/tdx: Add tdx_alloc/free_page() helpers Kirill A. Shutemov
2025-06-10 2:36 ` Chao Gao
2025-06-10 14:51 ` [PATCHv2.1 " Kirill A. Shutemov
2025-06-25 18:01 ` Dave Hansen
2025-06-25 20:09 ` [PATCHv2 " Dave Hansen
2025-06-26 0:46 ` Chao Gao
2025-06-25 20:02 ` Dave Hansen
2025-06-27 13:00 ` Kirill A. Shutemov
2025-06-27 7:49 ` Adrian Hunter
2025-06-27 13:03 ` Kirill A. Shutemov
2025-06-09 19:13 ` [PATCHv2 05/12] KVM: TDX: Allocate PAMT memory in __tdx_td_init() Kirill A. Shutemov
2025-06-09 19:13 ` [PATCHv2 06/12] KVM: TDX: Allocate PAMT memory in tdx_td_vcpu_init() Kirill A. Shutemov
2025-06-09 19:13 ` [PATCHv2 07/12] KVM: TDX: Preallocate PAMT pages to be used in page fault path Kirill A. Shutemov
2025-06-26 11:21 ` Huang, Kai
2025-07-10 1:34 ` Edgecombe, Rick P
2025-07-10 7:49 ` kirill.shutemov
2025-06-09 19:13 ` [PATCHv2 08/12] KVM: TDX: Handle PAMT allocation in " Kirill A. Shutemov
2025-06-12 12:19 ` Chao Gao
2025-06-12 13:05 ` [PATCHv2.1 " Kirill A. Shutemov
2025-06-25 22:38 ` [PATCHv2 " Edgecombe, Rick P
2025-07-09 14:29 ` kirill.shutemov
2025-07-10 1:33 ` Edgecombe, Rick P
2025-07-10 8:45 ` kirill.shutemov
2025-08-21 19:21 ` Sagi Shahar
2025-08-21 19:35 ` Edgecombe, Rick P
2025-08-21 19:53 ` Sagi Shahar
2025-06-09 19:13 ` [PATCHv2 09/12] KVM: TDX: Reclaim PAMT memory Kirill A. Shutemov
2025-06-09 19:13 ` [PATCHv2 10/12] [NOT-FOR-UPSTREAM] x86/virt/tdx: Account PAMT memory and print it in /proc/meminfo Kirill A. Shutemov
2025-06-09 19:13 ` [PATCHv2 11/12] x86/virt/tdx: Enable Dynamic PAMT Kirill A. Shutemov
2025-06-09 19:13 ` [PATCHv2 12/12] Documentation/x86: Add documentation for TDX's " Kirill A. Shutemov
2025-06-25 13:25 ` [PATCHv2 00/12] TDX: Enable " Kirill A. Shutemov
2025-06-25 22:49 ` Edgecombe, Rick P
2025-06-27 13:05 ` kirill.shutemov
2025-08-08 23:18 ` Edgecombe, Rick P
2025-08-11 6:31 ` kas
2025-08-11 22:30 ` Edgecombe, Rick P
2025-08-12 2:02 ` Sean Christopherson
2025-08-12 2:31 ` Vishal Annapurve
2025-08-12 8:04 ` kas
2025-08-12 15:12 ` Edgecombe, Rick P
2025-08-12 16:15 ` Sean Christopherson
2025-08-12 18:39 ` Edgecombe, Rick P
2025-08-12 22:00 ` Vishal Annapurve
2025-08-12 23:34 ` Edgecombe, Rick P
2025-08-13 0:18 ` Vishal Annapurve
2025-08-13 0:51 ` Edgecombe, Rick P
2025-08-12 18:44 ` Vishal Annapurve
2025-08-13 8:09 ` Kiryl Shutsemau
2025-08-13 7:49 ` Kiryl Shutsemau
2025-08-12 8:03 ` kas
2025-08-13 22:43 ` Edgecombe, Rick P
2025-08-13 23:31 ` Dave Hansen [this message]
2025-08-14 0:14 ` Edgecombe, Rick P
2025-08-14 10:55 ` Kiryl Shutsemau
2025-08-15 1:03 ` Edgecombe, Rick P
2025-08-20 15:31 ` Sean Christopherson
2025-08-20 16:35 ` Edgecombe, Rick P
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