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q->flows can be often modified, and q->timer_slack is read mostly.
Exchange the two fields, so that cache line countaining
quantum, initial_quantum, and other critical parameters
stay clean (read-mostly).
Move q->watchdog next to q->stat_throttled
Add comments explaining how the structure is split in
three different parts.
pahole output before the patch:
struct fq_sched_data {
struct fq_flow_head new_flows; /* 0 0x10 */
struct fq_flow_head old_flows; /* 0x10 0x10 */
struct rb_root delayed; /* 0x20 0x8 */
u64 time_next_delayed_flow; /* 0x28 0x8 */
u64 ktime_cache; /* 0x30 0x8 */
unsigned long unthrottle_latency_ns; /* 0x38 0x8 */
/* --- cacheline 1 boundary (64 bytes) --- */
struct fq_flow internal __attribute__((__aligned__(64))); /* 0x40 0x80 */
/* XXX last struct has 16 bytes of padding */
/* --- cacheline 3 boundary (192 bytes) --- */
u32 quantum; /* 0xc0 0x4 */
u32 initial_quantum; /* 0xc4 0x4 */
u32 flow_refill_delay; /* 0xc8 0x4 */
u32 flow_plimit; /* 0xcc 0x4 */
unsigned long flow_max_rate; /* 0xd0 0x8 */
u64 ce_threshold; /* 0xd8 0x8 */
u64 horizon; /* 0xe0 0x8 */
u32 orphan_mask; /* 0xe8 0x4 */
u32 low_rate_threshold; /* 0xec 0x4 */
struct rb_root * fq_root; /* 0xf0 0x8 */
u8 rate_enable; /* 0xf8 0x1 */
u8 fq_trees_log; /* 0xf9 0x1 */
u8 horizon_drop; /* 0xfa 0x1 */
/* XXX 1 byte hole, try to pack */
<bad> u32 flows; /* 0xfc 0x4 */
/* --- cacheline 4 boundary (256 bytes) --- */
u32 inactive_flows; /* 0x100 0x4 */
u32 throttled_flows; /* 0x104 0x4 */
u64 stat_gc_flows; /* 0x108 0x8 */
u64 stat_internal_packets; /* 0x110 0x8 */
u64 stat_throttled; /* 0x118 0x8 */
u64 stat_ce_mark; /* 0x120 0x8 */
u64 stat_horizon_drops; /* 0x128 0x8 */
u64 stat_horizon_caps; /* 0x130 0x8 */
u64 stat_flows_plimit; /* 0x138 0x8 */
/* --- cacheline 5 boundary (320 bytes) --- */
u64 stat_pkts_too_long; /* 0x140 0x8 */
u64 stat_allocation_errors; /* 0x148 0x8 */
<bad> u32 timer_slack; /* 0x150 0x4 */
/* XXX 4 bytes hole, try to pack */
struct qdisc_watchdog watchdog; /* 0x158 0x48 */
/* size: 448, cachelines: 7, members: 34 */
/* sum members: 411, holes: 2, sum holes: 5 */
/* padding: 32 */
/* paddings: 1, sum paddings: 16 */
/* forced alignments: 1 */
};
pahole output after the patch:
struct fq_sched_data {
struct fq_flow_head new_flows; /* 0 0x10 */
struct fq_flow_head old_flows; /* 0x10 0x10 */
struct rb_root delayed; /* 0x20 0x8 */
u64 time_next_delayed_flow; /* 0x28 0x8 */
u64 ktime_cache; /* 0x30 0x8 */
unsigned long unthrottle_latency_ns; /* 0x38 0x8 */
/* --- cacheline 1 boundary (64 bytes) --- */
struct fq_flow internal __attribute__((__aligned__(64))); /* 0x40 0x80 */
/* XXX last struct has 16 bytes of padding */
/* --- cacheline 3 boundary (192 bytes) --- */
u32 quantum; /* 0xc0 0x4 */
u32 initial_quantum; /* 0xc4 0x4 */
u32 flow_refill_delay; /* 0xc8 0x4 */
u32 flow_plimit; /* 0xcc 0x4 */
unsigned long flow_max_rate; /* 0xd0 0x8 */
u64 ce_threshold; /* 0xd8 0x8 */
u64 horizon; /* 0xe0 0x8 */
u32 orphan_mask; /* 0xe8 0x4 */
u32 low_rate_threshold; /* 0xec 0x4 */
struct rb_root * fq_root; /* 0xf0 0x8 */
u8 rate_enable; /* 0xf8 0x1 */
u8 fq_trees_log; /* 0xf9 0x1 */
u8 horizon_drop; /* 0xfa 0x1 */
/* XXX 1 byte hole, try to pack */
<good> u32 timer_slack; /* 0xfc 0x4 */
/* --- cacheline 4 boundary (256 bytes) --- */
<good> u32 flows; /* 0x100 0x4 */
u32 inactive_flows; /* 0x104 0x4 */
u32 throttled_flows; /* 0x108 0x4 */
/* XXX 4 bytes hole, try to pack */
u64 stat_throttled; /* 0x110 0x8 */
<better> struct qdisc_watchdog watchdog; /* 0x118 0x48 */
/* --- cacheline 5 boundary (320 bytes) was 32 bytes ago --- */
u64 stat_gc_flows; /* 0x160 0x8 */
u64 stat_internal_packets; /* 0x168 0x8 */
u64 stat_ce_mark; /* 0x170 0x8 */
u64 stat_horizon_drops; /* 0x178 0x8 */
/* --- cacheline 6 boundary (384 bytes) --- */
u64 stat_horizon_caps; /* 0x180 0x8 */
u64 stat_flows_plimit; /* 0x188 0x8 */
u64 stat_pkts_too_long; /* 0x190 0x8 */
u64 stat_allocation_errors; /* 0x198 0x8 */
/* Force padding: */
u64 :64;
u64 :64;
u64 :64;
u64 :64;
/* size: 448, cachelines: 7, members: 34 */
/* sum members: 411, holes: 2, sum holes: 5 */
/* padding: 32 */
/* paddings: 1, sum paddings: 16 */
/* forced alignments: 1 */
};
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.