From nobody Wed Mar 16 17:55:58 2022 X-Original-To: freebsd-fs@mlmmj.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mlmmj.nyi.freebsd.org (Postfix) with ESMTP id 3C14D1A21F94 for ; Wed, 16 Mar 2022 17:56:38 +0000 (UTC) (envelope-from karl@denninger.net) Received: from colo1.denninger.net (colo1.denninger.net [104.236.120.189]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 4KJdJ52Fnpz4l5D for ; Wed, 16 Mar 2022 17:56:37 +0000 (UTC) (envelope-from karl@denninger.net) Received: from denninger.net (097-081-026-048.res.spectrum.com [97.81.26.48]) by colo1.denninger.net (Postfix) with ESMTP id BB3F62110D1 for ; Wed, 16 Mar 2022 13:56:00 -0400 (EDT) Received: from [192.168.10.25] (D15.Denninger.Net [192.168.10.25]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by denninger.net (Postfix) with ESMTPSA id 4E9023F718C for ; Wed, 16 Mar 2022 13:56:00 -0400 (EDT) Message-ID: <3cca9997-97f7-7c49-9531-4069618539b1@denninger.net> Date: Wed, 16 Mar 2022 13:55:58 -0400 List-Id: Filesystems List-Archive: https://lists.freebsd.org/archives/freebsd-fs List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-fs@freebsd.org MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Content-Language: en-US To: freebsd-fs@freebsd.org From: Karl Denninger Subject: md option "async" risks kernel deadlock? Why. Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-512; boundary="------------ms080507080703090509080803" X-Rspamd-Queue-Id: 4KJdJ52Fnpz4l5D X-Spamd-Bar: --- Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=pass (policy=none) header.from=denninger.net; spf=pass (mx1.freebsd.org: domain of karl@denninger.net designates 104.236.120.189 as permitted sender) smtp.mailfrom=karl@denninger.net X-Spamd-Result: default: False [-3.91 / 15.00]; RCVD_VIA_SMTP_AUTH(0.00)[]; R_SPF_ALLOW(-0.20)[+mx]; HAS_ATTACHMENT(0.00)[]; TO_DN_NONE(0.00)[]; RCVD_COUNT_THREE(0.00)[3]; NEURAL_HAM_SHORT(-1.00)[-1.000]; DMARC_POLICY_ALLOW(-0.50)[denninger.net,none]; FROM_EQ_ENVFROM(0.00)[]; RCVD_TLS_LAST(0.00)[]; R_DKIM_NA(0.00)[]; ASN(0.00)[asn:14061, ipnet:104.236.64.0/18, country:US]; MID_RHS_MATCH_FROM(0.00)[]; SUBJECT_HAS_QUESTION(0.00)[]; RECEIVED_SPAMHAUS_PBL(0.00)[97.81.26.48:received]; ARC_NA(0.00)[]; FREEFALL_USER(0.00)[karl]; FROM_HAS_DN(0.00)[]; SIGNED_SMIME(-2.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; MIME_GOOD(-0.20)[multipart/signed,multipart/alternative,text/plain]; MIME_TRACE(0.00)[0:+,1:+,2:+,3:~,4:~]; PREVIOUSLY_DELIVERED(0.00)[freebsd-fs@freebsd.org]; NEURAL_SPAM_MEDIUM(0.99)[0.985]; RCPT_COUNT_ONE(0.00)[1]; MLMMJ_DEST(0.00)[freebsd-fs] X-ThisMailContainsUnwantedMimeParts: N This is a cryptographically signed message in MIME format. --------------ms080507080703090509080803 Content-Type: multipart/alternative; boundary="------------AOP6UJMcao4zF4E0KZ6YYGrS" --------------AOP6UJMcao4zF4E0KZ6YYGrS Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit From the man page for mdconfig(8)     -o [no]option              Set or reset options.              [no]async                      For vnode backed devices: avoid IO_SYNC for increased                      performance but at the risk of deadlocking the entire                      kernel. Why and how severe is this risk? The scenario where I care is the use of md to build and populate a "disk" image often used with Crochet and nanobsd so as to create an image file that can then be directly dd'd to a media device (e.g. SD card) and booted. When the backing store for this is a ZFS file on spinning rust the performance is beyond horrid; about 50tps is all you get, presumably due to clashes between the backing store and md itself which winds up forcing a crazy amount of seeks.  I suspect its seek-related because if the zfs pool is on SSD its plenty fast -- but a backing on spinning rust, including all mirror vdev-comprised pools (which are quite fast for general file storage) is silly-slow. Setting the zfs mountpoint to async has no impact on performance.  I assume that setting mdconfig's option very well might, but kernel deadlocks are bad news, so I'm trying to understand the risk profile since these builds are done on a production machine. Thanks! -- Karl Denninger karl@denninger.net /The Market Ticker/ /[S/MIME encrypted email preferred]/ --------------AOP6UJMcao4zF4E0KZ6YYGrS Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: 8bit

From the man page for mdconfig(8)

    -o [no]option
             Set or reset options.

             [no]async
                     For vnode backed devices: avoid IO_SYNC for increased
                     performance but at the risk of deadlocking the entire
                     kernel.

Why and how severe is this risk?

The scenario where I care is the use of md to build and populate a "disk" image often used with Crochet and nanobsd so as to create an image file that can then be directly dd'd to a media device (e.g. SD card) and booted.

When the backing store for this is a ZFS file on spinning rust the performance is beyond horrid; about 50tps is all you get, presumably due to clashes between the backing store and md itself which winds up forcing a crazy amount of seeks.  I suspect its seek-related because if the zfs pool is on SSD its plenty fast -- but a backing on spinning rust, including all mirror vdev-comprised pools (which are quite fast for general file storage) is silly-slow.

Setting the zfs mountpoint to async has no impact on performance.  I assume that setting mdconfig's option very well might, but kernel deadlocks are bad news, so I'm trying to understand the risk profile since these builds are done on a production machine.

Thanks!

--
Karl Denninger
karl@denninger.net
The Market Ticker
[S/MIME encrypted email preferred]
--------------AOP6UJMcao4zF4E0KZ6YYGrS-- --------------ms080507080703090509080803 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgMFADCABgkqhkiG9w0BBwEAAKCC DdgwggagMIIEiKADAgECAhMA5EiKghDOXrvfxYxjITXYDdhIMA0GCSqGSIb3DQEBCwUAMIGL MQswCQYDVQQGEwJVUzEQMA4GA1UECAwHRmxvcmlkYTESMBAGA1UEBwwJTmljZXZpbGxlMRkw FwYDVQQKDBBDdWRhIFN5c3RlbXMgTExDMRgwFgYDVQQLDA9DdWRhIFN5c3RlbXMgQ0ExITAf BgNVBAMMGEN1ZGEgU3lzdGVtcyBMTEMgMjAxNyBDQTAeFw0xNzA4MTcxNjQyMTdaFw0yNzA4 MTUxNjQyMTdaMHsxCzAJBgNVBAYTAlVTMRAwDgYDVQQIDAdGbG9yaWRhMRkwFwYDVQQKDBBD dWRhIFN5c3RlbXMgTExDMRgwFgYDVQQLDA9DdWRhIFN5c3RlbXMgQ0ExJTAjBgNVBAMMHEN1 ZGEgU3lzdGVtcyBMTEMgMjAxNyBJbnQgQ0EwggIiMA0GCSqGSIb3DQEBAQUAA4ICDwAwggIK AoICAQC1aJotNUI+W4jP7xQDO8L/b4XiF4Rss9O0B+3vMH7Njk85fZ052QhZpMVlpaaO+sCI KqG3oNEbuOHzJB/NDJFnqh7ijBwhdWutdsq23Ux6TvxgakyMPpT6TRNEJzcBVQA0kpby1DVD 0EKSK/FrWWBiFmSxg7qUfmIq/mMzgE6epHktyRM3OGq3dbRdOUgfumWrqHXOrdJz06xE9NzY vc9toqZnd79FUtE/nSZVm1VS3Grq7RKV65onvX3QOW4W1ldEHwggaZxgWGNiR/D4eosAGFxn uYeWlKEC70c99Mp1giWux+7ur6hc2E+AaTGh+fGeijO5q40OGd+dNMgK8Es0nDRw81lRcl24 SWUEky9y8DArgIFlRd6d3ZYwgc1DMTWkTavx3ZpASp5TWih6yI8ACwboTvlUYeooMsPtNa9E 6UQ1nt7VEi5syjxnDltbEFoLYcXBcqhRhFETJe9CdenItAHAtOya3w5+fmC2j/xJz29og1KH YqWHlo3Kswi9G77an+zh6nWkMuHs+03DU8DaOEWzZEav3lVD4u76bKRDTbhh0bMAk4eXriGL h4MUoX3Imfcr6JoyheVrAdHDL/BixbMH1UUspeRuqQMQ5b2T6pabXP0oOB4FqldWiDgJBGRd zWLgCYG8wPGJGYgHibl5rFiI5Ix3FQncipc6SdUzOQIDAQABo4IBCjCCAQYwHQYDVR0OBBYE FF3AXsKnjdPND5+bxVECGKtc047PMIHABgNVHSMEgbgwgbWAFBu1oRhUMNEzjODolDka5k4Q EDBioYGRpIGOMIGLMQswCQYDVQQGEwJVUzEQMA4GA1UECAwHRmxvcmlkYTESMBAGA1UEBwwJ TmljZXZpbGxlMRkwFwYDVQQKDBBDdWRhIFN5c3RlbXMgTExDMRgwFgYDVQQLDA9DdWRhIFN5 c3RlbXMgQ0ExITAfBgNVBAMMGEN1ZGEgU3lzdGVtcyBMTEMgMjAxNyBDQYIJAKxAy1WBo2kY MBIGA1UdEwEB/wQIMAYBAf8CAQAwDgYDVR0PAQH/BAQDAgGGMA0GCSqGSIb3DQEBCwUAA4IC AQCB5686UCBVIT52jO3sz9pKuhxuC2npi8ZvoBwt/IH9piPA15/CGF1XeXUdu2qmhOjHkVLN gO7XB1G8CuluxofOIUce0aZGyB+vZ1ylHXlMeB0R82f5dz3/T7RQso55Y2Vog2Zb7PYTC5B9 oNy3ylsnNLzanYlcW3AAfzZcbxYuAdnuq0Im3EpGm8DoItUcf1pDezugKm/yKtNtY6sDyENj tExZ377cYA3IdIwqn1Mh4OAT/Rmh8au2rZAo0+bMYBy9C11Ex0hQ8zWcvPZBDn4v4RtO8g+K uQZQcJnO09LJNtw94W3d2mj4a7XrsKMnZKvm6W9BJIQ4Nmht4wXAtPQ1xA+QpxPTmsGAU0Cv HmqVC7XC3qxFhaOrD2dsvOAK6Sn3MEpH/YrfYCX7a7cz5zW3DsJQ6o3pYfnnQz+hnwLlz4MK 17NIA0WOdAF9IbtQqarf44+PEyUbKtz1r0KGeGLs+VGdd2FLA0e7yuzxJDYcaBTVwqaHhU2/ Fna/jGU7BhrKHtJbb/XlLeFJ24yvuiYKpYWQSSyZu1R/gvZjHeGb344jGBsZdCDrdxtQQcVA 6OxsMAPSUPMrlg9LWELEEYnVulQJerWxpUecGH92O06wwmPgykkz//UmmgjVSh7ErNvL0lUY UMfunYVO/O5hwhW+P4gviCXzBFeTtDZH259O7TCCBzAwggUYoAMCAQICEwCg0WvVwekjGFiO 62SckFwepz0wDQYJKoZIhvcNAQELBQAwezELMAkGA1UEBhMCVVMxEDAOBgNVBAgMB0Zsb3Jp ZGExGTAXBgNVBAoMEEN1ZGEgU3lzdGVtcyBMTEMxGDAWBgNVBAsMD0N1ZGEgU3lzdGVtcyBD QTElMCMGA1UEAwwcQ3VkYSBTeXN0ZW1zIExMQyAyMDE3IEludCBDQTAeFw0xNzA4MTcyMTIx MjBaFw0yMjA4MTYyMTIxMjBaMFcxCzAJBgNVBAYTAlVTMRAwDgYDVQQIDAdGbG9yaWRhMRkw FwYDVQQKDBBDdWRhIFN5c3RlbXMgTExDMRswGQYDVQQDDBJrYXJsQGRlbm5pbmdlci5uZXQw ggIiMA0GCSqGSIb3DQEBAQUAA4ICDwAwggIKAoICAQC+HVSyxVtJhy3Ohs+PAGRuO//Dha9A 16l5FPATr6wude9zjX5f2lrkRyU8vhCXTZW7WbvWZKpcZ8r0dtZmiK9uF58Ec6hhvfkxJzbg 96WHBw5Fumd5ahZzuCJDtCAWW8R7/KN+zwzQf1+B3MVLmbaXAFBuKzySKhKMcHbK3/wjUYTg y+3UK6v2SBrowvkUBC+jxNg3Wy12GsTXcUS/8FYIXgVVPgfZZrbJJb5HWOQpvvhILpPCD3xs YJFNKEPltXKWHT7Qtc2HNqikgNwj8oqOb+PeZGMiWapsatKm8mxuOOGOEBhAoTVTwUHlMNTg 6QUCJtuWFCK38qOCyk9Haj+86lUU8RG6FkRXWgMbNQm1mWREQhw3axgGLSntjjnznJr5vsvX SYR6c+XKLd5KQZcS6LL8FHYNjqVKHBYM+hDnrTZMqa20JLAF1YagutDiMRURU23iWS7bA9tM cXcqkclTSDtFtxahRifXRI7Epq2GSKuEXe/1Tfb5CE8QsbCpGsfSwv2tZ/SpqVG08MdRiXxN 5tmZiQWo15IyWoeKOXl/hKxA9KPuDHngXX022b1ly+5ZOZbxBAZZMod4y4b4FiRUhRI97r9l CxsP/EPHuuTIZ82BYhrhbtab8HuRo2ofne2TfAWY2BlA7ExM8XShMd9bRPZrNTokPQPUCWCg CdIATQIDAQABo4IBzzCCAcswPAYIKwYBBQUHAQEEMDAuMCwGCCsGAQUFBzABhiBodHRwOi8v b2NzcC5jdWRhc3lzdGVtcy5uZXQ6ODg4ODAJBgNVHRMEAjAAMBEGCWCGSAGG+EIBAQQEAwIF oDAOBgNVHQ8BAf8EBAMCBeAwHQYDVR0lBBYwFAYIKwYBBQUHAwIGCCsGAQUFBwMEMDMGCWCG SAGG+EIBDQQmFiRPcGVuU1NMIEdlbmVyYXRlZCBDbGllbnQgQ2VydGlmaWNhdGUwHQYDVR0O BBYEFLElmNWeVgsBPe7O8NiBzjvjYnpRMIHKBgNVHSMEgcIwgb+AFF3AXsKnjdPND5+bxVEC GKtc047PoYGRpIGOMIGLMQswCQYDVQQGEwJVUzEQMA4GA1UECAwHRmxvcmlkYTESMBAGA1UE BwwJTmljZXZpbGxlMRkwFwYDVQQKDBBDdWRhIFN5c3RlbXMgTExDMRgwFgYDVQQLDA9DdWRh IFN5c3RlbXMgQ0ExITAfBgNVBAMMGEN1ZGEgU3lzdGVtcyBMTEMgMjAxNyBDQYITAORIioIQ zl6738WMYyE12A3YSDAdBgNVHREEFjAUgRJrYXJsQGRlbm5pbmdlci5uZXQwDQYJKoZIhvcN AQELBQADggIBAJXboPFBMLMtaiUt4KEtJCXlHO/3ZzIUIw/eobWFMdhe7M4+0u3te0sr77QR dcPKR0UeHffvpth2Mb3h28WfN0FmJmLwJk+pOx4u6uO3O0E1jNXoKh8fVcL4KU79oEQyYkbu 2HwbXBU9HbldPOOZDnPLi0whi/sbFHdyd4/w/NmnPgzAsQNZ2BYT9uBNr+jZw4SsluQzXG1X lFL/qCBoi1N2mqKPIepfGYF6drbr1RnXEJJsuD+NILLooTNf7PMgHPZ4VSWQXLNeFfygoOOK FiO0qfxPKpDMA+FHa8yNjAJZAgdJX5Mm1kbqipvb+r/H1UAmrzGMbhmf1gConsT5f8KU4n3Q IM2sOpTQe7BoVKlQM/fpQi6aBzu67M1iF1WtODpa5QUPvj1etaK+R3eYBzi4DIbCIWst8MdA 1+fEeKJFvMEZQONpkCwrJ+tJEuGQmjoQZgK1HeloepF0WDcviiho5FlgtAij+iBPtwMuuLiL shAXA5afMX1hYM4l11JXntle12EQFP1r6wOUkpOdxceCcMVDEJBBCHW2ZmdEaXgAm1VU+fnQ qS/wNw/S0X3RJT1qjr5uVlp2Y0auG/eG0jy6TT0KzTJeR9tLSDXprYkN2l/Qf7/nT6Q03qyE QnnKiBXWAZXveafyU/zYa7t3PTWFQGgWoC4w6XqgPo4KV44OMYIFBzCCBQMCAQEwgZIwezEL MAkGA1UEBhMCVVMxEDAOBgNVBAgMB0Zsb3JpZGExGTAXBgNVBAoMEEN1ZGEgU3lzdGVtcyBM TEMxGDAWBgNVBAsMD0N1ZGEgU3lzdGVtcyBDQTElMCMGA1UEAwwcQ3VkYSBTeXN0ZW1zIExM QyAyMDE3IEludCBDQQITAKDRa9XB6SMYWI7rZJyQXB6nPTANBglghkgBZQMEAgMFAKCCAkUw GAYJKoZIhvcNAQkDMQsGCSqGSIb3DQEHATAcBgkqhkiG9w0BCQUxDxcNMjIwMzE2MTc1NTU4 WjBPBgkqhkiG9w0BCQQxQgRAEnOzcbRhTvIeG13osOuLrWolrWq6Vb+78iibFEgx+e5+3CHy MbifTTCXgRpJpGxSypfYi3xXaT7m0sWwDzO86zBsBgkqhkiG9w0BCQ8xXzBdMAsGCWCGSAFl AwQBKjALBglghkgBZQMEAQIwCgYIKoZIhvcNAwcwDgYIKoZIhvcNAwICAgCAMA0GCCqGSIb3 DQMCAgFAMAcGBSsOAwIHMA0GCCqGSIb3DQMCAgEoMIGjBgkrBgEEAYI3EAQxgZUwgZIwezEL MAkGA1UEBhMCVVMxEDAOBgNVBAgMB0Zsb3JpZGExGTAXBgNVBAoMEEN1ZGEgU3lzdGVtcyBM TEMxGDAWBgNVBAsMD0N1ZGEgU3lzdGVtcyBDQTElMCMGA1UEAwwcQ3VkYSBTeXN0ZW1zIExM QyAyMDE3IEludCBDQQITAKDRa9XB6SMYWI7rZJyQXB6nPTCBpQYLKoZIhvcNAQkQAgsxgZWg gZIwezELMAkGA1UEBhMCVVMxEDAOBgNVBAgMB0Zsb3JpZGExGTAXBgNVBAoMEEN1ZGEgU3lz dGVtcyBMTEMxGDAWBgNVBAsMD0N1ZGEgU3lzdGVtcyBDQTElMCMGA1UEAwwcQ3VkYSBTeXN0 ZW1zIExMQyAyMDE3IEludCBDQQITAKDRa9XB6SMYWI7rZJyQXB6nPTANBgkqhkiG9w0BAQEF AASCAgB3xYHY8GdZnYZhecxcJ2UM+cpD4mroPet61d7DMQTnZ8QuBeyuXcg4w5tiohxPgFzi wTRcf3eWuGo1fh2Q8UrRwVZKE0rhMhbJiCyJXdHIeTVREXJHFTuGGrviGyQqcbbpX39JK7wr JzIdVP6002HIp4jicnNVL7eOpncfo5cW5PzPIgYTbSDacWLD8tArA60SY0tKK9KYqJB33+Yi +F8QNAqDKFkqKJYW6ZSYw11oIzj2Lh45C/XuGoUSk5A5OxttsgPfQV8DDbuimwQC0wbOCakw FBH5K0Dp+rS515ttXaDORS/l60JWZ5EapJmnax3n22pn4FvVFORWpo9rgPRqiJJC14lT5gNR m6LH0b4gK6YMB5sFBn3AJoVhuV19fykg+yFAsJ8lZGA5Fhbt67+tPdIXY2TeD0+Ey4E0XTq8 /RdW/KkSw9P6eaGS8zp/b5yGhOhVdVZhAdxyBXLz7pgzyp9ad1u5CIuWDIiM8rABdXJnMpsw j9nk4IBffTOPT2kU54lv53WVloIsokrNrlGR/oKidZTO3pPEdn8ox2Ns+pRjO5RcoS8/ZKPJ 4NDyhJ/UpFRfZNh5jQ1tkEUuQGxdbxLgH9gCtwI9Crxhu4gE5e99TPF9mc8+lUQn+e6qU7cg PeRvhOfNVpkhf2RNPkGaaPoig3RlGU0AqUZlKTchjwAAAAAAAA== --------------ms080507080703090509080803--