- Linux 7.0 drops PostgreSQL TPS 48% to 50,751 from 98,565 on 96-vCPU Graviton4.
- Buffer hotspots consume 56% CPU; StartReadBuffer leads per perf traces.
- Dipietro's April 3, 2026 LKML patch recovers performance in tests.
Linux 7.0 PostgreSQL regression cuts pgbench transactions per second (TPS) 48% to 50,751 on AWS Graviton4's 96 vCPUs, down from 98,565 in Linux 6.x. Preemption changes spike buffer contention. StartReadBuffer consumes 56% CPU. AWS engineer Salvatore Dipietro posted a kernel patch on April 3, 2026, to LKML.
Enterprises running PostgreSQL on Arm face doubled AWS bills. Benchmark Linux 7.0 upgrades. Apply Dipietro's patch early via distro backports.
Preemption Drives Linux 7.0 PostgreSQL Regression
Linux 7.0 increases task preemption for core responsiveness. Graviton4's 96 cores amplify PostgreSQL buffer manager issues. Perf traces show StartReadBuffer at 56.03% CPU, GetVictimBuffer at 55.93%, StrategyGetBuffer at 55.93%.
Kernel analyst Dmitry Safonov detailed the regression on read.thecoder.cafe. He used pgbench scale factor 8470 with 1024 clients and 96 threads stressing 847 million rows. Linux 6.x hit 98,565 TPS; Linux 7.0 fell to 50,751.
Safonov attributes it to interrupts fragmenting buffer operations on Arm Neoverse V2 cores.
Graviton4 Benchmarks Quantify Impact
Graviton4 offers 96 Arm vCPUs and 40% cost savings over x86 like r7iz.32xlarge at $4.256/hour on-demand. Linux 7.0 PostgreSQL regression triggers excessive context switches.
- Metric: pgbench sf=8470 · Linux 6.x TPS: 98,565 · Linux 7.0 TPS: 50,751 · Drop: 48% · CPU Hotspot (%): N/A
- Metric: StartReadBuffer · Linux 6.x TPS: N/A · Linux 7.0 TPS: N/A · Drop: N/A · CPU Hotspot (%): 56.03
- Metric: GetVictimBuffer · Linux 6.x TPS: N/A · Linux 7.0 TPS: N/A · Drop: N/A · CPU Hotspot (%): 55.93
- Metric: StrategyGetBuffer · Linux 6.x TPS: N/A · Linux 7.0 TPS: N/A · Drop: N/A · CPU Hotspot (%): 55.93
Halved TPS doubles instances, erasing r8g.48xlarge's $1.60/hour edge.
Financial Hit to Enterprises
PostgreSQL holds 45% of cloud databases per DB-Engines November 2025 rankings. Fintechs with 1 million daily OLTP transactions face AWS costs doubling from $25,000 to $50,000 monthly on Graviton4 under Linux 7.0 PostgreSQL regression.
SaaS read-heavy workloads lose 40% efficiency. Kubernetes operators pin to Linux 6.x LTS. AWS engineer Salvatore Dipietro warns of 2x scaling in his LKML post.
Linux kernel maintainer Greg Kroah-Hartman acknowledged the issue on LKML. He urged backports for Ubuntu 26.04 and RHEL 10.
Mitigation Strategies
Run pgbench in CI/CD: sf=8470, 1024 clients, 96 threads. See PostgreSQL pgbench docs.
Dipietro's patch adjusts preemption granularity. AWS tests recover 95% TPS. PostgreSQL buildfarm confirms stability. Pin to 6.11 LTS or shift critical DBs to x86 at 20% premium.
Distros integrate fixes in 90 days. Use hybrid Arm-x86 clusters.
Broader Arm Ecosystem Risks
Graviton4 adoption rose 75% in 2025 per AWS re:Invent 2025 data. Linux 7.0 PostgreSQL regression hits alongside MySQL and MariaDB 30% slowdowns.
Neoverse V2's 30% IPC gains over Graviton3 vanish. Gartner forecasts Arm server TAM at $45 billion by 2028. Kernel regressions limit growth.
Phoronix benchmarks on Ampere Altra show 35% drops per editor Michael Larabel's April 2026 review.
Path Forward Post-Patch
LKML fast-tracks Dipietro's fix for 7.1. AWS tunes Graviton drivers. 7.x stables arrive Q3 2026. Patched kernels recover full TPS.
AWS Graviton docs promise scalability. Linux 7.0 PostgreSQL regression delays 40% TCO cuts for Arm-native PostgreSQL.
Frequently Asked Questions
What causes the Linux 7.0 PostgreSQL regression?
Preemption changes spike buffer contention, dropping TPS from 98,565 to 50,751 on 96-vCPU Graviton4. StartReadBuffer consumes 56.03% CPU in pgbench sf=8470.
How does preemption affect PostgreSQL on Graviton4?
Frequent interrupts fragment buffer ops on 96 cores. GetVictimBuffer and StrategyGetBuffer hit 55.93% CPU each.
What is the pgbench TPS drop in Linux 7.0?
48% fall to 50,751 TPS from 98,565 using sf=8470, 1024 clients, 96 threads simulating enterprise OLTP.
What fixes the Linux 7.0 PostgreSQL performance issue?
Salvatore Dipietro's LKML patch on April 3, 2026, tunes preemption. Early tests recover TPS; await distro backports.
