[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Further issues Re: [PATCH for-4.17 v1 0/2] xenctrl.ml: improve scalability of domain_getinfolist
- To: Edwin Torok <edvin.torok@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- Date: Wed, 2 Nov 2022 17:26:10 +0000
- Accept-language: en-GB, en-US
- Arc-authentication-results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=citrix.com; dmarc=pass action=none header.from=citrix.com; dkim=pass header.d=citrix.com; arc=none
- Arc-message-signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=EDxHCF7Nmi72tXTpt26cinldWFyy5ix/bNnqKe/wfes=; b=TkviYj8whUrBr/9vyQfFESpbDL8oq1dsDrSoOS6VSMdmVnD0/xn+qOQ6h7QhiCclFLMx0VKefpLXuPz+sozZ1ooRm/IONDnkOMKddWZYmNyK7/YmQ8ZNRfN8yPVtaD6MQ9wh269uUhmbJR/Fj0GJ12qyHFKie7G43vjRnznZ8b8AR0xCCMCaAQ1+IeMJZtkZM/+B/WhP+MZM+jsXNO1SE2eOZBPPDg7kiiLSIdupZj3svKZ3OpQJxMFotmKzL4iYH5mbCN2RfYoRYNGY18/uRA+Nwtwz7pV0ST0fCrxh8lKvLec0MSg0ZBgPPVOB9rOKuq0xCsgcwFcTd+V1ojDEsQ==
- Arc-seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=k8Ep+YxUgkxsMwBql+EHJKYDTTihy67ESMflEkc27Jiauv9tcdysO5JEwmQTFkEOJJpOlcj99TSF4CMz+OyJF1Idt8/HuPowLRL3bYL8pTrdLW4/eRaA5mq+f/IMiI2+jBeI941o4wKrKj2zR5CLcUnwtpBKXCD8a/rIsCxHUU30qJWKPj4p6B0T7Du65+vnWiP7deTimn14RjXpwdKfHpTn1rH5qWqIx4GAtMC7naivnxl5pako1RWgsC/TPvBsN0robtCS4OgqmGURbhEIVi9sh/m3B49sA7pPEvxPVj1S1fOqubCwmXd/+e4D5SaU9/rEbnUbalo/4OCBs5x42Q==
- Authentication-results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=citrix.com;
- Cc: Pau Ruiz Safont <pau.safont@xxxxxxxxxx>, Christian Lindig <christian.lindig@xxxxxxxxxx>, David Scott <dave@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Anthony Perard <anthony.perard@xxxxxxxxxx>, Henry Wang <Henry.Wang@xxxxxxx>
- Delivery-date: Wed, 02 Nov 2022 17:26:34 +0000
- Ironport-data: A9a23:nNWuIqPHDl0QRPvvrR2YlsFynXyQoLVcMsEvi/4bfWQNrUp2gzIOn WNKC2uGa/uCY2ujed0laIixpExXu8CAm4RhSgto+SlhQUwRpJueD7x1DKtS0wC6dZSfER09v 63yTvGacajYm1eF/k/F3oDJ9CU6jufQA+KmU4YoAwgpLSd8UiAtlBl/rOAwh49skLCRDhiE/ Nj/uKUzAnf8s9JPGj9Suv/rRC9H5qyo4mpB5gZmP5ingXeF/5UrJMNHTU2OByOQrrl8RoaSW +vFxbelyWLVlz9F5gSNy+uTnuUiG9Y+DCDW4pZkc/HKbitq/0Te5p0TJvsEAXq7vh3S9zxHJ HehgrTrIeshFvWkdO3wyHC0GQkmVUFN0OevzXRSLaV/ZqAJGpfh66wGMa04AWEX0sluDGMU+ 7sWEigEPxWm2sGHxbenE/Y506zPLOGzVG8ekldJ6GmFSNwAEdXESaiM4sJE1jAtgMwIBezZe 8cSdTtoalLHfgFLPVAUTpk5mY9EhFGmK2Ee9A3T+vZxvze7IA9ZidABNPL8fNCQSNoTtUGfv m/cpEzyAw0ANczZwj2Amp6prr+UxHmhAdxOfFG+3sBEhASww30yMx9VanenkeWIlHahUM0Kf iT4/QJr98De7neDXtT7GhG1vnOAlhodQMZLVf037hmXzajZ6BrfAXILJhZNYcIrnNU7Tjsr0 hmOhdyBLSNrmK2YTzSa7Lj8hRO/PzIEa1ALYyAsRBEApdLkpekOYgnnS99iFOu/iI3zEDSon zSS9nBi2PMUkNIB0Li98RbfmTWwq5PVTwkzoALKQmai6QA/b4mgD2C11WXmAT97BN7xZjG8U LIswqByMMhm4UmxqRGw
- Ironport-hdrordr: A9a23:yrtGf6n67j2QuWYj2cLdiCpo0jHpDfOPimdD5ihNYBxZY6Wkfp +V8cjzhCWftN9OYhodcIi7SdK9qXO1z+8X3WGIVY3SETUOy1HYVr2KirGSjwEIeheOvNK1sJ 0NT0EQMqyWMbEXt6fHCUyDYq4dKbq8ge+VbIXlvhFQpGhRAskOgTuRSDzra3GeLzM2Z6bRYa Dsgvav0ADQHEj/AP7aOlA1G8z44/HbnpPvZhALQzQ97hOVsD+u4LnmVzCFwxY3SVp0sPYf2F mAtza8yrSosvm9xBOZ/XTU9Y5qlNzozcYGLNCQi/ISNi7nhm+TFcRcsvy5zXMISdOUmRMXee r30lMd1gNImjTsl1SO0FnQMs/boXATAjHZuAalaDDY0LHErXoBerZ8bMRiA1XkAgMbza9BOO gg5RPni7NHSRzHhyjz/N7OSlVjkVe1u2MrlaoJg2VYSpZ2Us4ZkWUzxjIjLH47JlON1Kk3VO 11SM3M7vdfdl2XK3jfo2l02dSpGnA+BA2PTEQOstGcl2E+pgEz82IIgMgE2nsQ/pM0TJdJo+ zCL6RzjblLCssbd7h0CusNSda+TmbNXRXPOmSPJkmPLtBOB1vd75rspLkl7uCjf5IFiJM0hZ TaSVtd8XU/fkr/YPf+qKGjMiq9NVlVcQ6duf22vaIJy4EUbICbQRGrWRQpj9aqpekZD4nSR+ uzUagmccPeEQ==
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHY7hvRP8qjKADr4EWYXnGWkvQZoK4r5CyA
- Thread-topic: Further issues Re: [PATCH for-4.17 v1 0/2] xenctrl.ml: improve scalability of domain_getinfolist
Hi,
To be clear, what is presented here are clear improvements in the status
quo, and qualify for inclusion on their own merits. And definitely
should be considered.
That said, this is a swamp with future problems, and one rather
fundamental one in Xen which I is not going to be easy to fix.
1) (simple), there are a bunch of stubs, including
stub_xc_domain_getinfo() which don't use
caml_{enter,leave}_blocking_section() when they should.
2) stub_xc_domain_getinfo() reuses xc_domain_getinfolist() meaning that
it uses XEN_SYSCTL_getdomaininfolist rather than
XEN_DOMCTL_getdomaininfo, which is a problem because...
3) While both of these hypercalls have crazy APIs leading to loads of
broken callers, at least the DOMCTL has a fastpath for when you specify
a valid domid. The SYSCTL (and DOMCTL slowpath) is an O(N) search of
all domains starting from d0 to find the first domain with an id >= the
input request.
The DOMCTL slowpath is useless. Not a single caller (I've ever
encountered) wants that behaviour, whereas I've needed to bugfix caller
which didn't have an "&& info.domid == domid" to have one, to get the
semantics they wanted. Cleaning this up will be a good improvement.
4) The (adjusted) algorithm in patch 1 still loops until it gets a
result with no entries. Meaning that it's still going to make one
hypercall too many, searching the entire domlist, to return no data. In
principle you could optimise to stop at any hypercall which returns
fewer than the requested number of domains, except...
5) ... if you ever use more than a single hypercall, Xen has dropped and
re-acquired the domlist read lock, meaning that you can't use the result
anyway. Causality couldn't be broken when domains were allocated
sequentially, but we have a random allocation mode now so you can
observe things out of order.
The only safe action is to ask for all 32k domains in a single go, and
use a single hypercall.
~Andrew
|
