Re: [RFC][PATCH 00/16] sched: Core scheduling

Mel Gorman
2019-02-22T12:45:52Z

On Mon, Feb 18, 2019 at 09:49:10AM -0800, Linus Torvalds wrote:
> On Mon, Feb 18, 2019 at 9:40 AM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > However; whichever way around you turn this cookie; it is expensive and nasty.
>
> Do you (or anybody else) have numbers for real loads?
>
> Because performance is all that matters. If performance is bad, then
> it's pointless, since just turning off SMT is the answer.
>

I tried to do a comparison between tip/master, ht disabled and this series
putting test workloads into a tagged cgroup but unfortunately it failed

[ 156.978682] BUG: unable to handle kernel NULL pointer dereference at 0000000000000058
[ 156.986597] #PF error: [normal kernel read fault]
[ 156.991343] PGD 0 P4D 0
[ 156.993905] Oops: 0000 [#1] SMP PTI
[ 156.997438] CPU: 15 PID: 0 Comm: swapper/15 Not tainted 5.0.0-rc7-schedcore-v1r1 #1
[ 157.005161] Hardware name: SGI.COM C2112-4GP3/X10DRT-P-Series, BIOS 2.0a 05/09/2016
[ 157.012896] RIP: 0010:wakeup_preempt_entity.isra.70+0x9/0x50
[ 157.018613] Code: 00 be c0 82 60 00 e9 86 02 1a 00 66 0f 1f 44 00 00 48 c1 e7 03 be c0 80 60 00 e9 72 02 1a 00 66 90 0f 1f 44 00 00
53 48 89 fb <48> 2b 5e 58 48 85 db 7e 2c 48 81 3e 00 00 10 00 8b 05 a9 b7 19 01
[ 157.037544] RSP: 0018:ffffc9000c5bbde8 EFLAGS: 00010086
[ 157.042819] RAX: ffff88810f5f6a00 RBX: 00000001547f175c RCX: 0000000000000001
[ 157.050015] RDX: ffff88bf3bdb0a40 RSI: 0000000000000000 RDI: 00000001547f175c
[ 157.057215] RBP: ffff88bf7fae32c0 R08: 000000000001e358 R09: ffff88810fb9f000
[ 157.064410] R10: ffffc9000c5bbe08 R11: ffff88810fb9f5c4 R12: 0000000000000000
[ 157.071611] R13: ffff88bf4e3ea0c0 R14: 0000000000000000 R15: ffff88bf4e3ea7a8
[ 157.078814] FS: 0000000000000000(0000) GS:ffff88bf7f5c0000(0000) knlGS:0000000000000000
[ 157.086977] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 157.092779] CR2: 0000000000000058 CR3: 000000000220e005 CR4: 00000000003606e0
[ 157.099979] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 157.109529] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 157.119058] Call Trace:
[ 157.123865] pick_next_entity+0x61/0x110
[ 157.130137] pick_task_fair+0x4b/0x90
[ 157.136124] __schedule+0x365/0x12c0
[ 157.141985] schedule_idle+0x1e/0x40
[ 157.147822] do_idle+0x166/0x280
[ 157.153275] cpu_startup_entry+0x19/0x20
[ 157.159420] start_secondary+0x17a/0x1d0
[ 157.165568] secondary_startup_64+0xa4/0xb0
[ 157.171985] Modules linked in: af_packet iscsi_ibft iscsi_boot_sysfs msr intel_rapl sb_edac x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel kvm ipmi_ssif irqbypass crc32_pclmul ghash_clmulni_intel ixgbe aesni_intel xfrm_algo iTCO_wdt joydev iTCO_vendor_support libphy igb aes_x86_64 crypto_simd ptp cryptd mei_me mdio pps_core ioatdma glue_helper pcspkr ipmi_si lpc_ich i2c_i801 mei dca ipmi_devintf ipmi_msghandler acpi_pad pcc_cpufreq button btrfs libcrc32c xor zstd_decompress zstd_compress raid6_pq hid_generic usbhid ast i2c_algo_bit drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops xhci_pci crc32c_intel ehci_pci ttm xhci_hcd ehci_hcd drm ahci usbcore mpt3sas libahci raid_class scsi_transport_sas wmi sg nbd dm_multipath dm_mod scsi_dh_rdac scsi_dh_emc scsi_dh_alua
[ 157.258990] CR2: 0000000000000058
[ 157.264961] ---[ end trace a301ac5e3ee86fde ]---
[ 157.283719] RIP: 0010:wakeup_preempt_entity.isra.70+0x9/0x50
[ 157.291967] Code: 00 be c0 82 60 00 e9 86 02 1a 00 66 0f 1f 44 00 00 48 c1 e7 03 be c0 80 60 00 e9 72 02 1a 00 66 90 0f 1f 44 00 00 53 48 89 fb <48> 2b 5e 58 48 85 db 7e 2c 48 81 3e 00 00 10 00 8b 05 a9 b7 19 01
[ 157.316121] RSP: 0018:ffffc9000c5bbde8 EFLAGS: 00010086
[ 157.324060] RAX: ffff88810f5f6a00 RBX: 00000001547f175c RCX: 0000000000000001
[ 157.333932] RDX: ffff88bf3bdb0a40 RSI: 0000000000000000 RDI: 00000001547f175c
[ 157.343795] RBP: ffff88bf7fae32c0 R08: 000000000001e358 R09: ffff88810fb9f000
[ 157.353634] R10: ffffc9000c5bbe08 R11: ffff88810fb9f5c4 R12: 0000000000000000
[ 157.363506] R13: ffff88bf4e3ea0c0 R14: 0000000000000000 R15: ffff88bf4e3ea7a8
[ 157.373395] FS: 0000000000000000(0000) GS:ffff88bf7f5c0000(0000) knlGS:0000000000000000
[ 157.384238] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 157.392709] CR2: 0000000000000058 CR3: 000000000220e005 CR4: 00000000003606e0
[ 157.402601] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 157.412488] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 157.422334] Kernel panic - not syncing: Attempted to kill the idle task!
[ 158.529804] Shutting down cpus with NMI
[ 158.573249] Kernel Offset: disabled
[ 158.586198] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---

RIP translates to kernel/sched/fair.c:6819

static int
wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se)
{
s64 gran, vdiff = curr->vruntime - se->vruntime; /* LINE 6819 */

if (vdiff <= 0)
return -1;

gran = wakeup_gran(se);
if (vdiff > gran)
return 1;
}

I haven't tried debugging it yet.

--
Mel Gorman
SUSE Labs