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Date: Tue, 25 Feb 2014 08:43:13 +0900
From: Minchan Kim <minchan@...nel.org>
To: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc: Jerome Marchand <jmarchan@...hat.com>,
Nitin Gupta <ngupta@...are.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv6 4/6] zram: add multi stream functionality
On Fri, Feb 21, 2014 at 02:50:41PM +0300, Sergey Senozhatsky wrote:
> This patch implements multi stream compression support.
>
> Introduce struct zcomp_strm_multi and a set of functions to manage
> zcomp_strm stream access. zcomp_strm_multi has a list of idle zcomp_strm
> structs, spinlock to protect idle list and wait queue, making it possible
> to perform parallel compressions.
>
> The following set of functions added:
> - zcomp_strm_multi_get()/zcomp_strm_multi_put()
> get and put compression stream, implement required locking
> - zcomp_strm_multi_create()/zcomp_strm_multi_destroy()
> create and destroy zcomp_strm_multi
>
> zcomp ->strm_get() and ->strm_put() callbacks are set during initialisation
> to zcomp_strm_multi_get()/zcomp_strm_multi_put() correspondingly.
>
> Each time zcomp issues a zcomp_strm_multi_get() call, the following set of
> operations performed:
> - spin lock strm_lock
> - if idle list is not empty, remove zcomp_strm from idle list, spin
> unlock and return zcomp stream pointer to caller
> - if idle list is empty, current adds itself to wait queue. it will be
> awaken by zcomp_strm_multi_put() caller.
>
> zcomp_strm_multi_put():
> - spin lock strm_lock
> - add zcomp stream to idle list
> - spin unlock, wake up sleeper
>
> Minchan Kim reported that spinlock-based locking scheme has demonstrated a
> severe perfomance regression for single compression stream case, comparing
> to mutex-based (https://lkml.org/lkml/2014/2/18/16)
>
> base spinlock mutex
>
> ==Initial write ==Initial write ==Initial write
> records: 5 records: 5 records: 5
> avg: 1642424.35 avg: 699610.40 avg: 1655583.71
> std: 39890.95(2.43%) std: 232014.19(33.16%) std: 52293.96
> max: 1690170.94 max: 1163473.45 max: 1697164.75
> min: 1568669.52 min: 573429.88 min: 1553410.23
> ==Rewrite ==Rewrite ==Rewrite
> records: 5 records: 5 records: 5
> avg: 1611775.39 avg: 501406.64 avg: 1684419.11
> std: 17144.58(1.06%) std: 15354.41(3.06%) std: 18367.42
> max: 1641800.95 max: 531356.78 max: 1706445.84
> min: 1593515.27 min: 488817.78 min: 1655335.73
> ==Random write ==Random write ==Random write
> records: 5 records: 5 records: 5
> avg: 1626318.29 avg: 497250.78 avg: 1695582.06
> std: 38550.23(2.37%) std: 1405.42(0.28%) std: 9211.98
> max: 1665839.62 max: 498585.88 max: 1703808.22
> min: 1562141.21 min: 494526.45 min: 1677664.94
> ==Pwrite ==Pwrite ==Pwrite
> records: 5 records: 5 records: 5
> avg: 1654641.25 avg: 581709.22 avg: 1641452.34
> std: 47202.59(2.85%) std: 9670.46(1.66%) std: 38963.62
> max: 1740682.36 max: 591300.09 max: 1687387.69
> min: 1611436.34 min: 564324.38 min: 1570496.11
>
> When only one compression stream available, mutex with spin on owner tends
> to perform much better than frequent wait_event()/wake_up(). This is why
> single stream implemented as a special case with mutex locking.
Side note:
It's true for x86 but it could be changed in embedded system like ARM
which is lower power compared to x86 and it also could depend on
compression algorithm speed so I am thinking we need adaptive locking
which sometime work with mutex sometime work with spinlock dynamically.
Anyway, it is further work and I should investigate more.
Most important thing is that this patchset wouldn't make any regression
if we use mutex for single stream as default so I'm okay now.
>
> In order to compile this functionality ZRAM_MULTI_STREAM config option
> required to be set, which will be introduced later.
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> ---
> drivers/block/zram/zcomp.c | 101 ++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 100 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
> index 9661226..41325ed 100644
> --- a/drivers/block/zram/zcomp.c
> +++ b/drivers/block/zram/zcomp.c
> @@ -12,9 +12,14 @@
> #include <linux/slab.h>
> #include <linux/wait.h>
> #include <linux/sched.h>
> +#ifdef CONFIG_ZRAM_MULTI_STREAM
> +#include <linux/spinlock.h>
> +#endif
Do we really need to include spinlock.h?
>
> #include "zcomp.h"
>
> +extern struct zcomp_backend zcomp_lzo;
> +
> /*
> * single zcomp_strm backend private part
> */
> @@ -23,7 +28,18 @@ struct zcomp_strm_single {
> struct zcomp_strm *zstrm;
> };
>
> -extern struct zcomp_backend zcomp_lzo;
> +#ifdef CONFIG_ZRAM_MULTI_STREAM
> +/*
> + * multi zcomp_strm backend private part
> + */
> +struct zcomp_strm_multi {
> + /* protect strm list */
> + spinlock_t strm_lock;
> + /* list of available strms */
> + struct list_head idle_strm;
> + wait_queue_head_t strm_wait;
> +};
> +#endif
>
> static struct zcomp_backend *find_backend(const char *compress)
> {
> @@ -63,6 +79,89 @@ static struct zcomp_strm *zcomp_strm_alloc(struct zcomp *comp)
> return zstrm;
> }
>
> +#ifdef CONFIG_ZRAM_MULTI_STREAM
> +/*
> + * get existing idle zcomp_strm or wait until other process release
> + * (zcomp_strm_put()) one for us
> + */
> +static struct zcomp_strm *zcomp_strm_multi_get(struct zcomp *comp)
> +{
> + struct zcomp_strm_multi *zp = comp->private;
How about comp->stream instead of private?
Other than that, Looks good to me.
> + struct zcomp_strm *zstrm;
> +
> + while (1) {
> + spin_lock(&zp->strm_lock);
> + if (list_empty(&zp->idle_strm)) {
> + spin_unlock(&zp->strm_lock);
> + wait_event(zp->strm_wait,
> + !list_empty(&zp->idle_strm));
> + continue;
> + }
> +
> + zstrm = list_entry(zp->idle_strm.next,
> + struct zcomp_strm, list);
> + list_del(&zstrm->list);
> + spin_unlock(&zp->strm_lock);
> + break;
> + }
> + return zstrm;
> +}
> +
> +/* add zcomp_strm back to idle list and wake up waiter */
> +static void zcomp_strm_multi_put(struct zcomp *comp, struct zcomp_strm *zstrm)
> +{
> + struct zcomp_strm_multi *zp = comp->private;
> +
> + spin_lock(&zp->strm_lock);
> + list_add(&zstrm->list, &zp->idle_strm);
> + spin_unlock(&zp->strm_lock);
> +
> + wake_up(&zp->strm_wait);
> +}
> +
> +static void zcomp_strm_multi_destroy(struct zcomp *comp)
> +{
> + struct zcomp_strm_multi *zp = comp->private;
> + struct zcomp_strm *zstrm;
> + while (!list_empty(&zp->idle_strm)) {
> + zstrm = list_entry(zp->idle_strm.next,
> + struct zcomp_strm, list);
> + list_del(&zstrm->list);
> + zcomp_strm_free(comp, zstrm);
> + }
> + kfree(zp);
> +}
> +
> +static int zcomp_strm_multi_create(struct zcomp *comp, int num_strm)
> +{
> + int i;
> + struct zcomp_strm *zstrm;
> + struct zcomp_strm_multi *zp;
> +
> + comp->destroy = zcomp_strm_multi_destroy;
> + comp->strm_get = zcomp_strm_multi_get;
> + comp->strm_put = zcomp_strm_multi_put;
> + zp = kmalloc(sizeof(struct zcomp_strm_multi), GFP_KERNEL);
> + comp->private = zp;
> + if (!zp)
> + return -ENOMEM;
> +
> + spin_lock_init(&zp->strm_lock);
> + INIT_LIST_HEAD(&zp->idle_strm);
> + init_waitqueue_head(&zp->strm_wait);
> +
> + for (i = 0; i < num_strm; i++) {
> + zstrm = zcomp_strm_alloc(comp);
> + if (!zstrm) {
> + zcomp_strm_multi_destroy(comp);
> + return -ENOMEM;
> + }
> + list_add(&zstrm->list, &zp->idle_strm);
> + }
> + return 0;
> +}
> +#endif
> +
> static struct zcomp_strm *zcomp_strm_single_get(struct zcomp *comp)
> {
> struct zcomp_strm_single *zp = comp->private;
> --
> 1.9.0.291.g027825b
>
> --
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--
Kind regards,
Minchan Kim
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