linux-kernel - Re: [PATCH 02/24] selftests/resctrl: Refactor fill

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Date:   Fri, 27 Oct 2023 14:41:36 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Maciej Wieczór-Retman 
        <maciej.wieczor-retman@...el.com>
cc:     linux-kselftest@...r.kernel.org,
        Reinette Chatre <reinette.chatre@...el.com>,
        Shuah Khan <shuah@...nel.org>,
        Shaopeng Tan <tan.shaopeng@...fujitsu.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 02/24] selftests/resctrl: Refactor fill_buf functions

On Fri, 27 Oct 2023, Maciej Wieczór-Retman wrote:

> On 2023-10-24 at 12:26:12 +0300, Ilpo Järvinen wrote:
> >There are unnecessary nested calls in fill_buf.c:
> >  - run_fill_buf() calls fill_cache()
> >  - alloc_buffer() calls malloc_and_init_memory()
> >
> >Simplify the code flow and remove those unnecessary call levels by
> >moving the called code inside the calling function.
> >
> >Resolve the difference in run_fill_buf() and fill_cache() parameter
> >name into 'buf_size' which is more descriptive than 'span'.
> >
> >Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> >---
> > tools/testing/selftests/resctrl/fill_buf.c | 58 +++++++---------------
> > tools/testing/selftests/resctrl/resctrl.h  |  2 +-
> > 2 files changed, 20 insertions(+), 40 deletions(-)
> >
> >diff --git a/tools/testing/selftests/resctrl/fill_buf.c b/tools/testing/selftests/resctrl/fill_buf.c
> >index f9893edda869..9d0b0bf4b85a 100644
> >--- a/tools/testing/selftests/resctrl/fill_buf.c
> >+++ b/tools/testing/selftests/resctrl/fill_buf.c
> >@@ -51,29 +51,6 @@ static void mem_flush(unsigned char *buf, size_t buf_size)
> > 	sb();
> > }
> > 
> >-static void *malloc_and_init_memory(size_t buf_size)
> >-{
> >-	void *p = NULL;
> >-	uint64_t *p64;
> >-	size_t s64;
> >-	int ret;
> >-
> >-	ret = posix_memalign(&p, PAGE_SIZE, buf_size);
> >-	if (ret < 0)
> >-		return NULL;
> >-
> >-	p64 = (uint64_t *)p;
> >-	s64 = buf_size / sizeof(uint64_t);
> >-
> >-	while (s64 > 0) {
> >-		*p64 = (uint64_t)rand();
> >-		p64 += (CL_SIZE / sizeof(uint64_t));
> >-		s64 -= (CL_SIZE / sizeof(uint64_t));
> >-	}
> >-
> >-	return p;
> >-}
> >-
> > static int fill_one_span_read(unsigned char *buf, size_t buf_size)
> > {
> > 	unsigned char *end_ptr = buf + buf_size;
> >@@ -137,20 +114,33 @@ static int fill_cache_write(unsigned char *buf, size_t buf_size, bool once)
> > 
> > static unsigned char *alloc_buffer(size_t buf_size, int memflush)
> > {
> >-	unsigned char *buf;
> >+	void *p = NULL;
> 
> Is this initialization doing anything? "p" seems to be either overwritten or in
> case of an error never accessed.

I'm aware of that but the compiler is too stupid to know that p is 
initialized if there's no error and spits out a warning so I'll have to 
keep the unnecessary initialization.

> >+	uint64_t *p64;
> >+	size_t s64;
> >+	int ret;
> > 
> >-	buf = malloc_and_init_memory(buf_size);
> >-	if (!buf)
> >+	ret = posix_memalign(&p, PAGE_SIZE, buf_size);
> >+	if (ret < 0)
> > 		return NULL;
> > 
> >+	/* Initialize the buffer */
> >+	p64 = (uint64_t *)p;
> >+	s64 = buf_size / sizeof(uint64_t);
> >+
> >+	while (s64 > 0) {
> >+		*p64 = (uint64_t)rand();
> >+		p64 += (CL_SIZE / sizeof(uint64_t));
> >+		s64 -= (CL_SIZE / sizeof(uint64_t));
> >+	}
> >+
> > 	/* Flush the memory before using to avoid "cache hot pages" effect */
> > 	if (memflush)
> >-		mem_flush(buf, buf_size);
> >+		mem_flush(p, buf_size);
> 
> Wouldn't renaming "p" to "buf" keep this relationship with "buf_size" more
> explicit?

I'll change it to buf. This patch has a long history which preceeds the 
change where I made the buffer ptr naming more consistent and I didn't 
realize I departed here again from the consistent naming until you now 
pointed it out.

-- 
 i.