RHEL Engineering is moving the tracking of its product development work on RHEL 6 through RHEL 9 to Red Hat Jira (issues.redhat.com). If you're a Red Hat customer, please continue to file support cases via the Red Hat customer portal. If you're not, please head to the "RHEL project" in Red Hat Jira and file new tickets here. Individual Bugzilla bugs in the statuses "NEW", "ASSIGNED", and "POST" are being migrated throughout September 2023. Bugs of Red Hat partners with an assigned Engineering Partner Manager (EPM) are migrated in late September as per pre-agreed dates. Bugs against components "kernel", "kernel-rt", and "kpatch" are only migrated if still in "NEW" or "ASSIGNED". If you cannot log in to RH Jira, please consult article #7032570. That failing, please send an e-mail to the RH Jira admins at rh-issues@redhat.com to troubleshoot your issue as a user management inquiry. The email creates a ServiceNow ticket with Red Hat. Individual Bugzilla bugs that are migrated will be moved to status "CLOSED", resolution "MIGRATED", and set with "MigratedToJIRA" in "Keywords". The link to the successor Jira issue will be found under "Links", have a little "two-footprint" icon next to it, and direct you to the "RHEL project" in Red Hat Jira (issue links are of type "https://issues.redhat.com/browse/RHEL-XXXX", where "X" is a digit). This same link will be available in a blue banner at the top of the page informing you that that bug has been migrated.
Bug 1322661 - The max number of vCPUs KVM supports is 256 currently, so libvirt needs to increase the open file descriptor limit
Summary: The max number of vCPUs KVM supports is 256 currently, so libvirt needs to in...
Keywords:
Status: CLOSED CURRENTRELEASE
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: doc-Virtualization_Tuning_and_Optimization_Guide
Version: 7.2
Hardware: Unspecified
OS: Unspecified
unspecified
unspecified
Target Milestone: rc
: ---
Assignee: Jiri Herrmann
QA Contact: ecs-bugs
URL:
Whiteboard:
Depends On: 1308395
Blocks:
TreeView+ depends on / blocked
 
Reported: 2016-03-31 03:24 UTC by yalzhang@redhat.com
Modified: 2019-03-06 01:59 UTC (History)
13 users (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Clone Of: 1308395
Environment:
Last Closed: 2016-11-07 17:22:20 UTC
Target Upstream Version:
Embargoed:
jherrman: needinfo-

Attachments (Terms of Use)

Comment 2 yalzhang@redhat.com 2016-04-07 03:29:48 UTC 
Sorry, I cloned this bug and did not modify it. Modified it as below and change the component to libvirt:
+++ This bug was initially created as a clone of Bug #1308395 +++

Version-Release number of selected component (if applicable):
Linux work 3.10.0-342.el7.x86_64 #1 SMP Thu Jan 14 18:52:04 EST 2016 x86_64 x86_64 x86_64 GNU/Linux
libvirt-1.3.3-1.el7.x86_64
qemu-kvm-rhev-2.3.0-31.el7_2.5.x86_64

Describe the issue: 
For virt-io multiqueue support, current kernel supports up to 256 rx queues, but when set to the "queues=251" or more, the guest fail to start. May be libvirt needs to increasethe open file descriptor limit (also known as "nofile" limit) for qemu by the number of queues.

How reproducible:
100%

Steps to Reproduce:
1.
# virsh dumpxml rhel7.2 | grep /interface -B4
    ...
      <driver name='vhost' queues='251'/>
      <address type='pci' domain='0x0000' bus='0x01' slot='0x01' function='0x0'/>
    </interface>
# virsh start rhel7.2
error: Failed to start domain rhel7.2
error: internal error: early end of file from monitor, possible problem: ((null):14879): SpiceDispatcher-ERROR **: dispatcher.c:260:dispatcher_init: socketpair failed Too many open files

when I set to 255, the guest can not start.
# virsh start rhel7.2
error: Failed to start domain rhel7.2
error: internal error: early end of file from monitor, possible problem: 2016-03-30T11:40:53.794624Z qemu-kvm: -netdev tap,fds=25:27:28:29:30:31:32:33:34:35:36:37:38:39:40:41:42:43:44:45:46:47:48:49:50:51:52:53:54:55:56:57:58:59:60:61:62:63:64:65:66:67:68:69:70:71:72:73:74:75:76:77:78:79:80:81:82:83:84:85:86:87:88:89:90:91:92:93:94:95:96:97:98:99:100:101:102:103:104:105:106:107:108:109:110:111:112:113:114:115:116:117:118:119:120:121:122:123:124:125:126:127:128:129:130:131:132:133:134:135:136:137:138:139:140:141:142:143:144:145:146:147:148:149:150:151:152:153:154:155:156:157:158:159:160:161:162:163:164:165:166:167:168:169:170:171:172:173:174:175:176:177:178:180:179:181:182:183:184:185:186:187:188:189:190:191:193:192:194:195:196:197:198:199:200:201:202:203:204:205:206:207:208:209:210:211:212:213:214:215:216:218:217:219:220:221:222:223:224:225:226:227:228:229:230:231:232:233:234:235:236:237:238:239:240:241:242:243:244:245:246:247:248:249:250:251:252:253:254:255:256:257:258:259:260:261:262:263:264:265:266:267:268:269:270:271:272:273:
Comment 3 Jaroslav Suchanek 2016-04-07 14:25:06 UTC 
Well, I moved it under documentation component, as I believe that number of open files is controlled by max_files option in the /etc/libvirt/qemu.conf configuration file and therefore it makes sense to document this specific use case in the related chapter.

Jirka, please confirm. Thanks.
Comment 4 Jiri Denemark 2016-04-07 15:05:40 UTC 
Yeah, I think documenting it is probably the right way to address this issue at this point.

Another thing is we could possibly change the limit ourselves based on domain XML, but that's a more complex task not limited to multiqueue. For example, we don't do it for disks either.
Note You need to log in before you can comment on or make changes to this bug.